The official selection for the festival and its sidebars are normally announced around the middle of April each year. Films showing in the festival sections (Competition, Out of Competition, Un Certain Regard, Cinéfondation, Cannes Classics) are announced in a press release on the official festival web site. But given the profile of the event, the selection hits most major new wires almost immediately.
Selections for the Directors' Fortnight and International Critics' Week are announced separately by their respective parent organisations; normally a day or two after the main festival selection is announced. Again, the announcements are made in a press release on the organisations' websites, and will appear in the trade press very soon afterwards.
Screening schedules and venues for films in the official programme and sidebars are normally released a week or two before the festival starts from the official websites. Thousands of other films are also shown in Cannes as part of the Market. Schedules are maintained and updated on a daily basis by the Market organisation, and released to the daily trades in Cannes every morning.
In order to attend an official screening in Cannes, you must hold festival or market accreditation. Market screenings are generally only open to market registrants and accredited members of the press.