To apply, visit https://secure2.comic-con.org/memberid/ and create a Member ID (if you don't already have one). Then, click the volunteer button on the bottom of the "Member ID Change Menu." This will bring you to the application page.
If you are selected to be a volunteer (returning volunteers get first priority, followed by new applicants in the order their applications were received), you will receive a confirmation 10 days after registration closes. Good luck!