The western (or full western) forehand grip is where the heel pad and index knuckle of your hitting hand are resting on the fifth bevel of the tennis racket. At 0:10 in the video, you can see a shot of me holding the racket with a western forehand grip, and you can see my heel pad and index knuckle resting on the fifth bevel of the tennis racket handle.
A shortcut to finding the western forehand grip is to hold your tennis racket at the throat in your non-hitting hand, out in front of you. Grab the racket with your hitting hand, and then turn your arm and the racket over. Your arm will be in a position similar to a “fist pump,” with the racket sticking out to the side. For a visual (easier to understand) explanation of this, watch the video above at 0:22.
If you hit with a western grip, your natural contact height will be high up around shoulder level. Also, if you hit with a western grip, you will be able to easily hit the ball with a ton of topspin, but it will be very hard for you to flatten the tennis ball out and drive it like you can with an eastern grip.