In the year of 1978, a slasher film was released titled Halloween.

The Halloween movie has its character, Michael Myers. When he was 6 years old, he murdered his sister using a mask to cover his face. His parents saw him covered in blood and saw that he murdered his sister then was put into a sanitarium under the care of Dr. Samuel Loomis. After 15 years he escapes the sanitarium and wreaks havoc on his town.

The Halloween had 9 movies and also 2 more which are Remakes but there is news that there would be 2 more which will be released in 2021 and another with no definite year yet. There are 4 ways to watch the Halloween franchise and understand how the story runs.

Order 1:
Halloween (1978)
Halloween II (1981)
Halloween H20: 20 Years Later (1998)
Halloween: Resurrection (2002)
Halloween (2018)

By watching Halloween and Halloween II you'll see who will he murder and understand the story, but by continuing to other franchises you'll see how the story progressed. During his murder spree in the town of Haddonfield, you'll see that he is targeting a teenaged girl named Laurie Strode. Who is Laurie Strode? Laurie is his younger sister whom he was not able to kill 15 years ago. In Halloween H20 it tells the story in a time frame after 20 years from Halloween II and also shows that Laurie has a son. The only error in this is that in Halloween H20 he has a son named John and in the Halloween released in 2018, she doesn't have a son but a daughter named Judy (which will also be seen in Halloween IV: Return of Michael Myers). 

I will not spoil more information about this one, but please stay tuned to other ways to watch the Halloween franchise.