When going on a modeling audition, your portfolio and resume most likely got you in the door. If you have a modeling agent, that agency will put together your portfolio and promote you to companies looking for new faces for their product. Depending on the product being sold, different jobs will require different looks for the situation. On a modeling audition you will be brought in to meet with the casting director or producer of the project being cast for.
They may take some test shots of you and meet with you briefly, but there is nothing more to prove than the right look. Unlike acting auditions, or singing auditions, your look and attitude alone will usually be what lands you the job. Models don't necessarily have to "act" if the look is right.