Fast-travel to Alpha Camp and meet Sam at the plantation. Follow him to the first bomb location and protect him while he's defusing it. Once done, head to the second location then use the ladder outside to climb the roof. Stay there and kill all enemies, including a technical.
Head to the last location and kill the two gunners there. Man the turret and use it to kill the pirates, including an attack chopper. The mission will be completed afterwards. Make sure to grab the ammo, health packs and armor lying around before leaving.