This is VERY simple, all you need is one (1) hand and one (1) erect (and preferably uncircumcized, else you'll need a lubricant) penis.
You take your 4 fingers (index through pinky) and put them along the base of your shaft. Then, put your thumb (That short 'extra' finger that we humans have) and put it on the top of your shaft. Lightly squeeze and slide your hand up and down.
This grip is execellent because you can easily switch from this to a full fist, or to two fingers (index and thumb). It provides great control over speed and pressure, I've been known to masturbate for an over an hour before climaxing! It's also completely lube-free (unless you're circumcized)!!
Enjoy, and happy fapping!