Screenplay format is something that a lot of people have problems with. Screenplay format is not like any other type of writing. And you have to get it just right. You can use a program like Final Draft to help you out with this. But some people just use Microsoft Word. There is also a free program called Celtx.
Here is a resource for screenplay format: Stop Writing Crap!. You can also have a look at the Nicholl Fellowship page as it gives an example of proper format.