how to copyright a short film?

Under the federal law, you get a copyright to your work automatically once you have "fixed" your original work in a "tangible medium of expression." You must have independently created the work and not adapted it from something else. The work must also be placed in a sufficiently permanent medium so others can reproduce, view or communicate it. Thus you cannot simply create a film and store it in your room. It must be placed somewhere where others can see it.

Although the copyright comes automatically, there are still a number of reasons why you should formally register your copyright. You are limited in your remedies if you do not properly register the copyright.

For example, copyright registration will affect:

Lawsuits - If you are a U.S. copyright owner, you must register your copyright before initiating an action for copyright infringement

Damages - You cannot get damages for infringement for any period before the copyright is registered

Evidence - The registration of copyright, in addition to some other criteria, is proof of the validity of a copyright

You can register your copyright here:

http://www.copyright.gov/eco/

How To Copyright A Film

It's already copyrighted. It was copyrighted the moment you created it. A copyright can't stop people from stealing it. All it does it provide a cause of action to sue for an injunction or damages in the event that someone does steal it.