The first thing to do is go to www.AmericanIdol.com. Search the sites listed auditions to find one near you.
You need to download, print, and fill out the release from found on their website. Bring it to the auditions along with a few forms of ID showing that your a legal American citizen between the ages of 16 and 18.
A few days before the audition, register online. You can do this on the same site you went to earlier.
Be sure to prepare well for your audition and arrive early. There are many people that come to auditions so getting there as early as possible will help guarantee you a spot in the audition room.
Now you just have to wait till your called in the room. Do your best to impress the judges and sing your heart out. If your good you'll get a pass to move on to the next round. Good luck on becoming Americas next idol.