Speak with Fiona to get this mission (do exactly the same with following tasks). Your job is to get back stolen cargo with weapons. Each gun will give you $500.
To run GPS in your PDA [#036] get into the car [#035] and follow instructions.
Reach a destination point, kill some enemies (especially this one on the boat with heavy machine gun) and steal the truck [#037].
Try to drive in a slowly and steady way. Otherwise, machine guns will start drop out and you will lose money.
Next to the city entrance venezuelan army will send some troops and armed jeeps. You will encounter some barricades inside the city as well; peaceful evading should to the trick. Stop in the marked area [#038] and leave the lorry to finish the mission.
Payment: depends on the number of brought guns and it can reach even $9.500