This is pretty much an assured achievement that you will unlock as you progress through the game. Possible spoiler warning, just want to put you on your guard.
Once you get to Mother Base for the first time and have gone through the tutorial with Ocelot, he will give you your Fulton Recovery System. When out in the field all you need to do to extract a soldier is to get close to them and hold the Y button. But be careful, if you suddenly begin extracting someone who is guarding an outpost he will shout for his friends to come and help him. Either knock the target out or take out the other guards in the area to make sure you don't cause yourself any trouble. As a general rule its a good idea to subdue your target before using the Fulton and then making sure there isn't anyone around who will see or hear the balloon.
After a few missions of extracting everyone you see you'll have earned this achievement. Hope I helped.