After your escape of the Pillar of Autumn you land on a mysterious ring world. Once you have crashed, Cortana will ask you if your alright. Pick up all the ammo and health and make your way across the bridge to your left. A covenant dropship will arrive to look for survivers. Contine to run if you dont want to fight them. While your running Banshees will also show up. Take out one of them with your pistol. That should cause the other one to fly away. Make your way down the rocksides and to the huge structure on the other side.
Once your there, fight the covenant and talk to your fellow marines. After you have talked to them there will be a big fight. Continue to fight until no more covenant arrive. Cortana will signal in a Pelican Dropship to evac survivers. The dropship will also drop a warthog off for you.
Take the warthog and drive down to the tunnels and proceed through them until you reach an area filled with covenant. Let your gunner wipe out all of them and then get out of the jeep and run up the path to the right of the entrance. There will be an elite or two waiting for you. Kill them. Proceed down the path and click the control panel to turn on the bridge. After you have done that, drive across it and make your way out of the tunnels.
Once out of the tunnel, drive up the high hill and enter on of the three rock wall openings to rescue fellow soldiers. Continue to the second opening and then finally the third. For one of them, there will an underground part. You might have to go underneath and rescue your soldiers. Clear all three areas and save as many soldiers as you can. Once this is done you have completed the level! Next up...Truth and Reconciliation.