When your agent or a casting agency calls you about a part in Film, they will tell you the location, date and time and send you pages from the Film's script (sides) if they are available. Producers and casting directors choose pages from the script that will showcase the character being read for. If the role is comedic, the audition content will be a comedic scene.
Many times, especially as an actor becomes more experienced, they may read for multiple roles depending on the play. If the film is about six high school kids and you are reading for one of the girls, you may be asked to read for more than one role. If you know this is in advance, make sure to review all the roles. Usally a casting director will have you read for a different part on the spot, without you knowing prior. Stay calm. Just read the lines and try your best. The director knows you aren't rehearsed for that role and many actors end up landing parts they weren't even called in for.
In the audition it is okay to ask where to look once you begin, especially if there is no camera in the room. Usually an actor should perform in the direction of the casting director so he/she can see your face. But don't make eye contact with them. This makes casting directors uncomfortable because some may feel they have to acknowledge your performance.
You may read directly from the pages you are given. The main goal in a Film audition is to nail the content and read what the page says. You will have time to rehearse if you land the part, but in the audition, pay attention to the content given.
If you get suggestions from the casting director on how to read, THAT'S GOOD! This means the director is interested and you have caught his/her attention. Take the suggestions in stride, and do what is requested, after all, the director is whom you are trying to impress.
When finished, say thank you to everyone in the room. Even the person operating the camera, and the PA who got you water. No matter what your audition was like, leave making a good impression as a person, and as a professional. And remember, don't call them, they'll call you.