This is the information for a particular college, use it as a guideline, not legal advise.
You must obtain a Public Performance License (typical range: $300.00 - $500.00) for the individual film(s) from a licensing agent, which allows you the right to screen the film publicly.
There are, however, a few exceptions.
1. The film is in the Public Domain.
2. You have written permission from the film’s producer or other holder of the right to grant such permission.
3. The film is obtained from a company that provides a Public Performance License with the purchase of the film. These films are most often documentary in nature, and typically do not include commercial or theatrically released films.
Companies that provide a Public Performance License with DVD or Video purchase include:
Media Education Foundation
Listed on MEF website: In addition, all purchased videos and DVDs are licensed for classroom viewing and public screening where no admission is charged.
All Filmmakers Library, Inc. titles, for sale or rental, include public performance rights.
First Run/Icarus Films
From their site: "Videos purchased from First Run/Icarus Films are licensed with Public Performance Rights for non-commercial and educational exhibition when no admission fee is charged."
PS. If you are charging money that is a whole different ballgame.