Print out the confirmation. One of several options will happen.
The ADR turnstile is all the way to the right, and well marked. Show up at 8am or slightly earlier.
1. A cast member will have a list of names, ask you yours, and you will be waved in after inserting your park ticket.
2. Nobody will say anything. You enter the turnstile and you will be on your way. Oddly enough, at Magic Kingdom this is the scenario I have had most. (Yes, no checks in any way were given to allow early entrance. Maybe I just looked like I knew what I was doing)
3. You will have to show your confirmation number, and will then be let in.