You have to wait in line before hand to get wrist bands which are exchanged for tickets at the door. I dont know the specifics this year but normally they do it the night before for each draft day. So day 2 wristbands will be given out at the end of day 1. No one really cares about day 3 and you can just walk up and get a ticket. I recommend trying to get in early so you can get a gift bag that has some football cards, a radio to listen to the NFLN/ESPN screens they project inside and other swag.
This is the first year I'm not going in a while so I'm a little bummed. Also you can look on craigslist for people selling wrist band/tickets. There is a good amount of people who wait in line just to flip them for a profit.