Level 2 - Flawless Cowboy
Level 2 comprises of two chapters.
 Flawless Cowboy
When you start the level, make your way out of the pod and grab some ammo and grenades from the ground outside. There will be a bridge spanning the canyon to your right. When you start to cross it, Cortana will warn you that there's Covenant armour heading your way. A Banshee and a Covenant Dropship will arrive shortly. It's best to try to avoid them as a Pistol and an Assault Rifle aren't sufficient defense against Banshees on anything harder than Easy.
Once you've dodged your way through those, continue up the hill and take out the Covenant resistance. There will be some human survivors over the hill, and once you meet them you will trigger a wave of about 3 more dropships. Take out any Covenant that land, being careful not to hit the Marines, because they will turn into enemies if you hurt them too much. After you've cleared the area of any incoming Covenant, a Pelican ((Echo 419)), will arrive and drop a Warthog for you. Get in and take any survivors you saved with you. If you look to the sky after you get the Warthog, you will see more drop pods coming in to land nearby. This is your cue to go to the rescue. Driving off through the Covenant base where you just picked up your survivors will lead you to a river. There are 2 drop ships to be collected.
The first drop ship will be straight across the river when you come out from the initial area where you got the warthog. You will see the way lit by two small blue beacons. When you go through, you will find another Covenant base, again, you will have to defend the marines until all the Covenant have been driven back so you can call for an Evac for them. Once that's done, get back in your Warthog and go back out the way you came in. On the opposite side of the river you passed, further down, there will be another path, just like the one leading to the area you just came out of. When you go through here, you will find yet another Covenant base. Go inside the structure to find your comrades. When you come back up, you guessed it, more Covenant Dropships will be there to greet you. Take them all out yet again. Your efforts will be rewarded with yet another evacuation Pelican for the surviving marines.
 Reunion Tour
So you've just rescued some more Marines, take your warthog and head to the back of the area you are in. There will be a sharp drop, leading down to a large cave. This is obviously a Covenant cave. Follow the cave down until you come into a large Atrium. Once you pull up at the big gorge in the middle, get out, head back the way you came on foot. To your left as you come off the bridge, there will be a doorway. Be careful for the jackals and Elites in the area. Go in the door, it will lead you up a ramp. Be careful again because there is a sneaky elite waiting around the corner to surprise you. Take them out and continue to the end of the walkway. This will lead you to a control console. When you activate it, you will see the brdige where you left your warthog come online and turn into a solid form. Return to your Warthog and go across the bridge and out the other side of the Covenant Structure.
From the cave you just exited, there will be an exit to the North, at the top of the hill. Take your Warthog and keep diving until you come to an open area with a lot or large rocks. Before you arrive, Cortana will inform you that the Pillar Of Autumn's crash site has been completely overrun by Covenant, and they cannot raise Captain Keyes on any form of Communication.
The area you just arrived in will have human survivors among the large rocks. Again, you have to protect them against waves of Covenant assault. There will be about 5 drop ships this time. Once you're done, Cortana will contact you again to tell you that they located where they are keeping the troops they captured from the Pillar of Autumn. They're being kept on a Covenant Warship close by, called Truth and Reconciliation.
This time, when the Pelican comes to collect the survivors, you will be going with them, ending the level.