This is quick. Hit the door opener - checkpoint.

Now tons of wasp guys come in after you - shoot them down. These are the drones. After you take those out, another group of land troops will come after you. When you're clear - checkpoint - "concentrate fire on first carrier"

Now you're in another area with a massive elevator area and a turret. You hear that the first carrier ignored us and headed straight for earth.

Halo 2 Walkthrough

Halo 3 Walkthrough