The parade starts at the front (by Sid Cahuenga's) and stops at the hat. Now the 501st and Rebel Legion groups (not Disney) continue on and exit thru the gate by Star Tours (they are only allowed to march from the entrance to the exit by ST) the rest of the characters (Chewbacca, Leia, Ahsoka,etc) stop and stay at the Hat with the celeb. host and visiting celebrities, the host welcomes everyone on stage and then they have a few moments with everyone for a photo op.
The parade starts with the JTA kids and Jedi Masters, they stay at the bottom part of the stage by the hat, then the 501st and Rebel Legion groups march thru and then the rest of the characters and celebrities arrive at the Hat.
After the welcome ceremony the characters go backstage by The Great Movie Ride and the celebs get back in the convertibles and drive back down Hollywood Blvd to where the parade started.
I hope this is clear, here's a link from last years parade:
http://www.youtube.com/watch?v=7Z1qtRzVDt4
here's a link to the welcome ceremony:
http://www.youtube.com/watch?v=51LCF8dtKMs