First open the door and then get the warthog, then you just drive until you get to the bridge section, where you drive up the hill that's right next to the bridge, and then when you get to barrier, you can optionally get a grav lift in the huts to make the bridge jump easier. You just drive up to the barrier, throw a nade at it, and then make your way to the bridge.
Bridge Jump: So there are multiple ways of doing this jump, the fastest way is to just squeeze your warthog inbetween the concrete barriers, but the more safe approach is to get a grav lift and use that to just fly over the concrete barriers.
After that you just keep driving until you get to the section with the 2 brutes and the 2 choppers, you get one of the choppers, drive to the left until you get under the road, and then drive up the hill on the left, drive to the ending section, kill the shade, and destroy the barrier to end the level.
TODO: explain driving up the hill with the chopper better.