Halo Walkthrough: I would have been your daddy
You're dropped off on a ledge, deep inside Halo. This level is nice because there are glowing white arrows that lead you directly to where you want to go. Just follow the glowing arrows :)
You hit a few fights, then you're out in a snowy bridge area. At the end of the bridge is a sword guy, four grenades will take him out. Then you're in a big room with windows. To the left is medical gear, an assault weapon and ammo. Continue on to the door.
You take an elevator down, and now you're in an open snowy area. There are marines here to save. Hop into the ghost so you get unlimited ammo, and take out the enemies. Now move forward to the Scorpion. All the marines will hop onto the sides of it. Pretty cool! Cross to the door. You have to jump out to open the door, then jump back in.
Cross the bridge - there are lots of cannons to take out. Then open the door on the other side.
Master Halo Walkthrough