In the movie, a gang of ten World War II veterans led by Danny Ocean (Sinatra) rob five different Las Vegas casinos, (the Sands, the Dunes, the Flamingo, the Riviera, and the Sahara) on a single New Year's Eve[?] night.
They make excuses to their wives and head for Vegas.
Warning: Wikipedia contains spoilers.
The Rat Pack plans the elaborate heist with the precision of an Army operation. Sammy gets a job driving a garbage truck while others get jobs working the various casinos. Still another plants demolition charges on an electrical transmission tower. At exactly midnight New Year's Eve[?], when everyone in every Vegas casino is singing Auld Lang Syne[?] (in unison), the tower is blown up, Vegas goes dark, and the inside men sneak into the cashier's cages and stick up the cashiers. They dump the bags of loot in the hotel's garbage bin, go back inside and mingle with the crowd; when Auld Lang Syne is over, the lights come back on and the robbers walk out of the casino.
But one of them has a heart attack in the middle of Las Vegas Boulevard[?] and dies. Meanwhile, Cesar Romero, who is some sort of operator known to all the casino bigwigs, offers to recover the money for the casino bosses for a cut. He also happens to know Danny Ocean and his wife (who has arrived in Vegas for some reason). Romero manages to piece together the puzzle by the time the dead team member is buried. In the end, the money gets cremated along with the dead guy.
The picture is best remembered for the time spent hangin' with the Rat Pack.
In this picture, Clooney et al. plan to rob the Bellagio[?], Mirage and MGM Grand[?], all of whom store their money in a central, hi-tech vault. The casino boss (played by Garcia) is currently dating Clooney's ex-wife. The robbers foil the elaborate security mechanisms to get to the vault with the casino's money, and escape by disguising themselves as the SWAT team.
Other than the main character (Danny Ocean), none of the robbers in the second movie share names with robbers in the first, although they do exhibit some of their personal quirks.