A convent asks people to spiritually adopt a voting cardinal.

As observers and Vatican insiders speculated on what caused such an extraordinarily long first evening session — with a stemwinder of a meditation from the former preacher of the papal household and a lack of Italian language skills among new cardinals slowing things down — the cardinals, still bound by oaths of secrecy and stripped of phones and internet access, reconvened.

On Thursday, crowds were gathering in St. Peter’s Square as the cardinals prepared to vote as often as twice in the morning and twice in the afternoon. If the first vote of the morning yields a winner, white smoke will pour out of the chimney atop the Sistine Chapel, the signal that a new pope has been chosen. If no one captures two-thirds of the cardinal electorate, the prelates vote again. If the result is inconclusive, as it was on Wednesday night, it will be signaled with a stream of black smoke. The cardinals would then break for lunch, and probably some politicking, and repeat the process.

Pope Francis’ death in April set in motion the process of choosing his successor, the first conclave in more than a decade. The papal election is one of the world’s oldest dramas, but this one is unlike any other. It is the largest ever assembled, and many cardinals appointed by Francis are meeting one another for the first time.

The new faces bring unfamiliar politics, priorities and concerns that some experts say could make the selection process more fragmented than usual. Francis also left the church deeply divided, with progressive factions pushing for more inclusion and change, and conservatives seeking to roll things back, often under the guise of preserving unity.

Here’s what to know:

• How it works: Except for Wednesday, when there was only one vote, the cardinals will participate in four rounds of voting every day until a candidate achieves a two-thirds majority. The ballots are burned up to twice a day, once in the morning and once in the afternoon, and smoke emitted from a purpose-built chimney above the Sistine Chapel signals the result — black smoke for no decision, white if there is a pope.

• How long it takes: There is no indication of how long the conclave will go, though the last two conclaves reached decisions within two days. One in the 13th century dragged on for almost three years.

• Extreme secrecy: Some security experts say the conclave is the most secure vote anywhere. The closed-door process, which is designed to be leakproof, has been fine-tuned over the centuries.

• Referendum on Francis: The election in many ways will turn on whether the cardinals want a pope who will follow Francis’ path of openness and inclusion or forge a different one. During his 12-year pontificate, Francis made landmark declarations that encouraged liberals, including allowing the blessing of people in same-sex unions and raising his voice for migrants.

People can sign up at a local church in Rimini or through the website of the convent, which houses a community of Poor Clares, also known as the Clarisses.

The nuns have been clear that it is not a popularity contest. “We specify that this not a poll nor a Toto-Papa,” the website says, referring to the term for papal election predictions much used by Italian journalists. “We are not inviting people to choose the one who will become pope, but rather a cardinal to accompany with a special prayer in the election of the pope.”

According to the site, all 133 cardinals have been adopted by at least one person. As of Thursday morning, 1,173 people had made a choice.

No word on who has the most prayers.

Lorena Belloso, 48, from Argentina and her husband were among the few in the square. “We came for a vacation to Spain and Italy, but we are Catholic believers and now we are waiting for the new pope,” she said. “It’s a historic moment.”

On Wednesday evening, tens of thousands of people packed the square to wait for the outcome of the first ballot. A result had been expected early in the evening, but it wasn’t until 9 p.m. that black smoke rose from the chimney, signaling that the cardinals had not reached a consensus on a new pope. Applause, cheers and gasps of disappointment broke out among the crowd, which quickly vacated the square.

The last major changes to the rules came in 1996 and were laid out in a document written by Pope John Paul II, “Universi Dominici Gregis: On the Vacancy of the Apostolic See and the Election of the Roman Pontiff.”

Before a single vote was cast on Wednesday, the chapel was cleared of all but the cardinal electors. (This time there are 133 of them.) The room was swept for listening and transmission devices. The windows were boarded up. Jamming devices are routinely used, to ensure that the proceedings cannot be interfered with, or snooped on.

The participants all took an oath to uphold the sanctity — and, in essence, the security — of the vote. The process is almost entirely tech-free: Cardinals write their votes by hand on paper ballots, and then proceed one at a time to the altar to place their ballots in an urn.

Nine cardinals oversee the process. Three are known as “scrutineers,” tasked with counting and recounting the votes and three are “revisers” who double-check their work.

All of this creates “enormous social — religious, actually — disincentives to hacking the vote” or leaking details, Bruce Schneier, a security expert and lecturer at Harvard Kennedy School, wrote in a 2005 blog post.

Twenty years later, with smartphones and recording devices nearly everywhere, Mr. Schneier reflected on the security of the voting. In an interview last week, he said that he still considered the conclave to be nearly hackproof. (On a scale of one to 10, with 10 being unhackable, Mr. Schneier gave it a 9.9.)

“It’s a small manual process, which makes it more secure,” he added. But that also makes it nearly impossible to replicate for national elections. “There are no lessons for the real world,” he said, “because it doesn’t scale.”

In the 13th century, the tradition of sequestering the cardinals during the conclave started after residents in Viterbo, near Rome, where it was being held, grew frustrated with a selection process that dragged on almost three years.

Locals locked the squabbling cardinals in the papal palace in Viterbo and had the roof removed, subjecting them to the elements. They also cut down their food rations until they made a selection. Pope Gregory X finally emerged as their choice after 33 months.

It’s no wonder that Gregory X scrambled to come up with fixed rules for the conclave, which comes from the Latin “with key.” They included reducing meals to one a day if a pope was not elected after three days, and to only bread and water after five more days.

But some papal elections continued to drag on. In the 17th and 18th centuries, European Catholic monarchies used their influence over loyal cardinals to shape the outcome, meaning that votes sometimes dragged on for months.

Conclaves have become considerably shorter in the past two centuries, after the end of the pope’s temporal power in 1870.

The last two popes, Francis and Benedict XVI, were each elected within two days.

Cardinals provided varying estimates of how long this conclave would last. Some said the process may take longer than recent selections because the members of the large and diverse College of Cardinals, many of them appointed by Pope Francis in recent years, don’t know each other well.

Cardinal Timothy M. Dolan of New York said he thought the conclave would be longer than the one that elected Francis. He has packed 12 packets of peanut butter, and enough to eat three a day.

“I think it’ll be longer than last time,” he said.

Others predict the cardinals will converge on a well-known name and wrap it up fast.

“Everyone says that, but I don’t know how they know,” Cardinal Anders Arborelius of Sweden said in a recent interview. Maybe, he said, “Everyone wants to get home as soon as possible.”

Josh Holder and Elizabeth Dias contributed reporting.

If neither vote is successful, the next two ballots will take place around 5:30 p.m. and 7 p.m. on Thursday.

Casting, reading and incinerating the secret ballots can take a while, so those times are only estimates.

The voting procedure is precisely choreographed. All 133 voting cardinals must write the name of the man he sees as pope on a rectangular piece of paper under the phrase “Eligo in Summum Pontificem,” or “I elect as the supreme pontiff.” Cardinals individually walk their ballots to the chapel’s altar, where they say an oath in Latin, and leave the ballot on a plate.

Votes are counted before being read aloud and pierced and tied together with a red string (the “Conclave” film depicted this practice). After ballots are counted, they are burned.

Smoke emerges from the Sistine Chapel up to twice a day, once in the morning and once in the afternoon. Black smoke tells the world that the cardinals haven’t reached a decision; white smoke announces that a new pope has been chosen.

Both of the past two popes — Benedict XVI in 2005 and Francis in 2013 — were elected in two days. For the past two centuries, each pope was selected within four days or fewer.

The cardinal electors will take Sunday off for prayer if a pope has not been selected by Saturday afternoon.

Here’s a look at some of those objects, and the meaning behind them.

Voting Instruments

When the cardinals vote in the Sistine Chapel, they will be sitting in rows of simple wooden tables. At one end of the chapel, a large table is set up for those who run the voting, according to the Universi Dominici Gregis, or U.D.G., one of the documents used to govern the papal transition.

The room also contains voting instruments, including an urn to receive the ballots, a set of wooden balls, and a needle and twine. The urn is used to collect the ballots, rectangular pieces of paper printed with the Latin phrase “Eligo in Summum Pontificem” (“I elect as Supreme Pontiff”).

The ballots contain a space where each cardinal writes in the name of his chosen candidate. The ballots are placed in the urn and are removed for counting after all the cardinals have voted.

The wooden balls are used to keep track of the ballots. The balls have numbers written on them that correspond to the number of cardinals voting in the conclave. As the ballots are being counted, an attendant removes one of the wooden balls for each ballot, to ensure that the number matches the number of cardinals, according to The Catholic Advocate, formerly a newspaper of the Archdiocese of Newark, N.J. If the numbers don’t match, the ballots must be burned without being read and another vote is conducted immediately, according to the U.D.G.

As the ballots are being read, they are pierced with the needle through the word “Eligo” and strung onto the thread, “so that the ballots can be more securely preserved,” according to the U.D.G.

The Oath of Secrecy

The conclave is a secretive institution, and many steps are taken to prevent leaks, including restricting the cardinals’ use of phones, the internet and newspapers.

The members of the College of Cardinals, the body that will elect the pope, must also swear and sign an oath of secrecy, according to the U.D.G. The oath reads, in part: “I will observe absolute and perpetual secrecy with all who are not part of the College of Cardinal electors concerning all matters directly or indirectly related to the ballots cast and their scrutiny for the election of the Supreme Pontiff.”

The cardinals also must promise not to record anything in Vatican City during the time of the election. The punishment for breaking the oath is “automatic” excommunication, according to the oath.

The Stove

The weekend before the conclave began, Vatican workers installed a simple stove in which ballots would be burned in the Sistine Chapel. Fire crews also installed a chimney on the roof of the chapel, where the smoke will leave the building.

After each round of voting, the ballots are mixed with chemicals that, when burned, emit either black or white smoke. Black smoke means that the cardinals have not yet reached the requisite majority; white smoke means that a new pope has been elected and voting is over.

The Seal

At the beginning of the conclave, the Apostolic Palace, which contains the Sistine Chapel, is closed to the public. On Wednesday, members of the Pontifical Swiss Guard placed beaded ropes with the guard’s seal at the entrances to the palace to ensure privacy and maintain secrecy for the cardinals.

The Vatican City government also planned to deactivate cellphone service within its territory for the duration of the conclave, starting on Wednesday afternoon.

The Papal Vestments

After a pope is elected, he is taken to the “Room of Tears,” a small room next to the Sistine Chapel, where he will put on the white papal cassock for the first time. Garments in three sizes are prepared and kept in the room, since no one knows who — or what size — the next pope will be.

The room is known as the “Room of Tears” because there are accounts of previous popes becoming overwhelmed with emotion in the room, and being moved to tears, after their election. After the pope puts on the vestments, he is introduced to the public for the first time.