If you don't know how to start, simply pick ant note you like, I would suggest seventh freth on the G string.

Pick it, just as you use to do, then just touch the string with your thumb on the same place on the string you picked, almost as when you take a natural harmonic and you will hear the harmonic.. Then do it again, but faster now. Later on, you will be able to pick harmonics easly.. Remember, pinch harmonics sounds different, depending on where you take them on the string..

Good luck!