Making a finger joint, or a box joint, using a table saw jig is done by flushing the board against the plug. Learn how to make a finger joint in this free woodworking video.
Before I make my first cut, I like to take a piece of masking tape and put it across the backside of the board so it covers about three quarters of an inch. And this is going to help; this is going to help keep the board from tearing out and getting a real torn up cut. As you can see, this edge of the board right here that was cut on a table saw with no tape. And you don't want to have this rough edge here when you cut your pins, so this piece of tape will help keep this wood from tearing out. To make the outside pin cut, I'm going to put my board flush up against the plug. Hold it firmly to the jig, and make my cut. And move the board over, and set it right down on that plug. And this is what holds it in place to make sure that your next cut is the same size and the same distance. This is what we have when we're done. This is going to be a front piece on the box. It could be side piece, it could be a front piece, but whatever, you're going to need two of your pieces cut like this, and two of your pieces are going to be cut like this. This is the one that has the shoulder instead of the pin here, so it fits inside, like that. So to make this cut, I'm just going to flip my scrap over, and get the other half inch square block that I cut that we talked about before, and put it right up, next to this, butt it up there, like we did in the beginning. Slide this board up next to it, and make sure they're firmly against each other, and then we're going to make that cut.