what is the story of Resident Evil ???

In the 1960s, the progenitor virus was established. The 3 scientists that made it founded Umbrella Corporation to excuse their research. 2 scientists died due to mysterious natural causes and murder. Some guy named Albert Wesker, from Umbrella Corporation, went undercover in Racoon City Police Department's S.T.A.R.S. Team.
Meanwhile, Umbrella Corporation went evil and started dealing Biological Terrorism devices that would turn people into zombies. S.T.A.R.S. members Wesker, Jill Valentine, and Chris Redfield were forced into a zombie-infested mansion. After fighting their way through, they discovered Wesker was evil. Jill and Chris destroyed the mansion, but Wesker escaped.
Racoon City was turned into zombies. Leon S. Kennedy, a police officer, helped Chris' sister Claire escape. Claire, unaware of her brother's whereabouts, was rather frantic.
Chris was in Europe trying to end Umbrella Corporation.
Jill was still in Raccoon City, trying to escape the newly ruined and zombie infested town. The U.S. Government heard of the zombie crisis, so they sent a nuclear missile to blow up Raccoon City. Jill barely escaped the city.
Claire and Chris were reunited. The U.S. Government discovered Umbrella's secrets, so they shut it down. After the U.S. Secret Service heard of Leon S. Kennedy's actions in Raccoon City, they hired him as an agent, and sent him to rescue the President's daughter. Biological Terror takes a huge positive bump here, as a cult takes control of many European rural citizens, using a Bio-Terrorist virus. Kennedy escapes with the President's daughter.

That is the history up to the end of Resident Evil 4. If you purchase Resident Evil 5, you may go to the "Library" Menu-Tab, and look at the full history of Resident Evil.