The first movie had very little to do with the games, aside from a setting and some names.
RESIDENT EVIL: The first game has to do with some mysterious murders near Raccoon City, an American metropolis of unnamed location. The police department gets a lead that something weird is happening at a mansion outside of town, owned by the Umbrella Corporation. An elite strike/investigation team, the STARS, is assembled to fly out there in a helicopter and recon the area.
Things go wrong; one of the STARS is killed by what appear to be skinless dogs, and the chopper pilot panics and flees. Four others are trapped in the mansion – Team Leader Wesker, Barry, Jill, and Chris.(you have the option of playing the game as Jill or Chris; the game is slightly different, depending on which you choose).
The games are sort of a third-person sort of thing, something like Tomb Raider, but without the ability to jump; the emphasis is on combat and puzzle-solving.
It turns out that the mansion is an Umbrella Corporation research center, and they were working on a virus weapon that kills, then reanimates human beings and dogs. The virus has even weirder effects on other creatures – you encounter killer ravens the size of hawks, “Hunters,” which resemble a cross between an ape and a frog, with large and nasty claws, gigantic spiders, and lots of other terrifying things. Oh, yeah, and LOTS of flesh-eating zombies. Your mission is to survive, gather your surviving teammates, gather information about the place, and escape in one piece.
RESIDENT EVIL II: Takes place a short time after the first Resident Evil, perhaps only days. Chris’s sister Claire has come to town looking for him, and rookie cop Leon has arrived for his first day on duty with the Raccoon City police force. Their timing really stinks. You may play as either Claire or Leon; the game is very different, depending on who you play, and it includes a sequel option, which means if you play as Leon first, then you play as Claire, your actions as Leon affect what happens to Claire! You really have to play this one through FOUR times to really find all the surprises.
Much of the game takes place in the devastated Raccoon City Police Department. It turns out that a far more virulent form of the virus escaped, and has turned the population of Raccoon City into zombies… and worse. What’s even worse, the Umbrella Corporation scientist who developed the virus shot himself up with a megadose of the stuff… and continues to show up, scare the hell out of you, and try to kill you periodically through the game, mutating into something bigger and meaner every time. Acknowledged by many as the best of the original PS1 RE games.
RESIDENT EVIL III: NEMESIS: Jill returns, and she’s trapped in Raccoon City, now quarantined by the government; no one gets in or out. She must fight her way out of the city, not only against the viral horrors and zombies, but against a team of Umbrella mercenaries ostensibly sent in to help the survivors!
…and what’s worse, one of the viral horrors is under the control of Umbrella – the monster called Nemesis – and his mission is to kill anyone who knows of Umbrella’s connection to the virus. Even more fun, in order to stop the spread of the virus, the government has decided saturation nuclear bombing of Raccoon City is the only way to be certain…
I haven’t played any of the remakes or sequels after Part III: Nemesis, but that’s the gist of it. From what I saw, the first movie was a mix of concepts from (mostly) the first game with a few from the second game. The second movie (which I have yet to see) seems to be based largely on the second and third games, in that all of Raccoon City is now infected…