The usual course is to find the website for the festival and you will then click on SUBMIT FILM. On that page they will have a SUBMISSION FORM, where you put in the name of the movie, your name and contact info, run time, formats, etc.
Then you mail this submission form with the check or money order for the submission fee. Then you wait until they announce the movies. Several good festivals will email you to let you know if you got rejected (or get in).
Or most festivals have the SUBMIT VIA WITHOUT A BOX and it's a lot more automated.