OK first a quick section with only a few enemies so you get the hang of this. Then fly to your big friend's nose for checkpoint.

Now comes the fun part, the flying, following and shooting. Watch where he shoots and get the enemies there. There are a few flying guys, a few turrets, a few land based enemies, and so on. Just keep going on. "This area is clear - let us continue." A few more to kill. Checkpoint. More shooting, then "clear that landing zone."

You'll get a marker to follow, go to it and shoot everything down there, then land. When you get them all, checkpoint. The door now opens and you see all of your fellow troops heading in for the assault.

Halo 2 Walkthrough

Halo 3 Walkthrough