How to fulton extract ?
It's pretty simple, during you first arrival at the Mother Base, Ocelot will teach you how to extract an enemy soldier on the battlefield, you'll then be able to do it from chapter 3.
First, the enemy must be inconscient (Asleep / Knock Out) and outside (no roof above his head). Then you just have to press
near his body and the guy will fly away to your Mother Base. To maximize your chances of succeeding the extraction, the weather has to be good (no sandstorm or whatever).
It is told "an enemy soldier", thus it won't work with the wolves you meet at the very beginning of chapter 3