This is how I first started to masterbate when I was younger. It works best in briefs, or with nothing at all.
To start if wearing briefs get hard and position your penis so the head is straight up, tenting the briefs. Then make a tight fist with your thumb along the side. Hold your penis with your other hand and rub the head between the second and third knuckle, that is the ones closet to your fingertips. It may take a while, but it is enjoyable, especially if you're new to masterbating.