After the previous mission, you'll jump out of the helicopter and have to land on the ground. Start making your way to the next marker, which is northwest of Delta Camp. When you get to Sam, he'll take the gunner position while you will drive.
Your objective is to blow up 4 areas with planted C4. When you plant each one, you will have 20 seconds to escape the blast area before they go off. Start with the southeastern one. The C4 spot is in a long fenced-in area, and as soon as you get in, two normal enemies as well as a Heavy with a LMG will appear. Kill them, then plant the charge and get out of there, killing the enemies that will appear on your exit.
The next one is the northeastern one. Be careful of bringing Sam along for this one, as there's an enemy with a RPG nearby. As you approach the reserve, some normal enemies will show up. Go around the fence at the east end to find the path to the C4 spot, as well as a Heavy with a Flamethrower. Take him out, plant the charge and get out there.
The next one is the southwestern one. Kill the enemies around the building, then go around the east side to the back to find a ladder. Climb it and you'll be right outside the window of the building where the C4 spot is located, although there are plenty of enemies inside, including a Heavy with a LMG. Go inside when it's clear, killing the rest of the enemies, then going down the stairs near the window you entered. Plant the charge, then get out of the building the same way you used to enter.
The last one is the northwestern one. When you approach it, a vehicle with a Machine Gun will pull up, so kill all of the men. This spot is wide open, so there's no secret path needed to access it. Plant the charge, then run out and enemies will come from both sides of the road.
Once that is over, you need to drive Sam to the fuel reserve maintenance building. Sam tells you to man the machine gun while he goes in, so go to the back of the vehicle. There will be a lot of enemies that come after you, from both entry points. This includes vehicles with machine guns and normal enemies on foot. Eventually, a helicopter will even arrive, which should warrant your full attention.
It is best to not use the sights on the machine gun, as it limits your view somewhat. Not long after the helicopter is shot down, Sam will get in the vehicle and drive away. While he's driving, shoot the barrels to dwindle the numbers a bit and when he jumps off a ramp, the mission will be over.
