In total, there have been 10 Halloween movies released from 1978 through 2009 (4 of these were released in the 1980's). Focusing on the original 1978 movie, which starred Jamie Lee Curtis, as Laurie Strode, in her first professional role, was an extremely low budget film that turned a mega-huge profit (it received mostly positive reviews).
In the original, a lunatic Michael Myers escapes the mental hospital he had been put into, years earlier, for murdering his older sister. The next day being Halloween, Michael decides to dress in blue overalls and a white mask, and then return to the town of Haddonfield, Illinois, where he had killed his sister as a 6 year old.
Michael begin stalking a young baby sister name Laurie (Curtis), and begins killing Laurie's neighborhood friends. When Michael corners Laurie and tries to kill her, she eventually gets the upper hand, and manages to hurt him just long enough to get away which allows Michael's psychiatrist to put 6 bullets in his body. At the end of the movie, when the group tries to find Michael's body, it is gone...And that is why there were so many more movies.