The first few missions are pretty linear and you can't really stray from them until you go to Motherbase and then return to Afghanistan. Now you can do SIDE OPS. I really recommend getting the interpreter ASAP it will make everything a lot easier.
You will be dropped off pretty close to the guy and there are only three there crawl through the grass until you're about 20m away from them and tranq the lot. May as well take all of them with you so go ahead and fulton them and OP is complete.