Canon 332 §2 of the Code of Canon Law states: “If it happens that the Roman Pontiff resigns his office, it is required for validity that the resignation is made freely and properly manifested but not that it is accepted by anyone.”
So, since the Pope has not died, there will not be the period of mourning and Masses, the Novemdiales, the day of death being counted as one of the days.
When the Pope resigns, at 8 p.m. Rome time on 28 February, there will be a state called “sede vacante”, “the see being empty” . I remind priests not to say the Pope’s name in the Eucharistic Prayer after that.
Most curial offices cease and must be reconfirmed. One office that continues is that of the Major Penitentiary, because his office concerns internal forum matters and, thus, the care of souls in urgent situations.
Governance of the Church devolves to the College of Cardinals meeting in Congregations, General and Particular. All cardinals, even those over 80, who are not legitimately impeded (by weather, illness, government interference, etc.) should attend, though older men can get permission not to. The General Congregations are lead by the Dean or Sub-Dean, or the senior Elector. The powers of the Congregations are limited by what the previous Pope prescribed. Particular Congregations are smaller groups of cardinals tasked to handle pressing needs of governance. This includes the Camerlengo, and a Cardinal Bishop, Cardinal Priest and Cardinal Deacon who are chosen by lot from the electors (cardinal under 80) who are in Rome. They have terms of three days. A Particular Congregation can’t overturn the work of a previous Particular Congregation.
Ordinarily a conclave begins on the 15th day after the death of the Pope, though it can be pushed back to 20 for serious reasons. Given that there is no Novemdiales period, the conclave could start around 9-10 March.
After the electors take their oaths, those who cannot vote are expelled from the conclave (the famous “extra omnes”). Only a few assitants can stay in the conclave’s confines. Nine electors are chosen by lot to work as Scrutineers (who do the tabulation and watch over the ballots as they are delivered), Infirmarii (who take ballots to and from cardinals who may be ill within the conclave) and Revisers (who check the count and make sure the voting was done right). When ballots are counted, they are strung together by a thread. They were once burned, famously with wet straw to produce black smoke if there was no election. In 1963 chemicals were added to make really dark or light smoke. In 2005 the bells of St. Peter’s Basilica were rung to signal an election.
There is one ballot on the first day, two on subsequent days.
Benedict XVI changed some of the voting rules. John Paul II had elminated the 2/3 majority rule in 1996 and Benedict XVI restored it in 2007.
Benedict XVI was elected after 4 ballots.
Benedict will not participate in the conclave to elect his successor (wow.. it is strange to write that).