The whole idea of casting is what creates the need for headshots in the first place. If you're a first time actor, you need to understand how the whole casting process goes before you get into acting.
Casting, simply defined, is the act of choosing an actor for a role. The process, on the other hand, is much more complicated and is what's most important for you to understand.
The casting process works as follows:
1. You submit your headshot, the best one you think would work for the role you are trying to get. You can either mail in a hard copy or do an online submission, both of which work.
2. If the casting director who reviews your headshot likes what he sees (meaning that you like like the character they imagined could play the role), you may be called in for an audition. This will typically happen via telephone or email. Usually, auditions take place over the course of a few days, and for some projects, there are open auditions, meaning you can just walk in whenever you arrive. For other projects, auditions are scheduled at specific times.
3. If you do well in your audition, you may be called back. Typically, you are asked to bring in another headshot to your callback. The callback audition is much more in depth and the casting director is much more critical. They have narrowed it down to only a few top choices for the role, so the competition is fierce. Be sure to put on your A-game and be confident.
4. Assuming you did a great job, some places may hold a second round of callbacks and perhaps even more. But typically, the selected actor will be chosen for the role and you will sign some papers indicating you are being paid to act in something, and failure to show up for it could result in some penalty.
After the papers have been signed, the casting process is complete and you have been cast in the role!