Tongue and Groove Joinery

With one edge of each board jointed (either with a jointer or using a table saw jointer jig), the next step is to rip the opposite edges so that they're perfectly parallel to the jointed edge.

Set up your table saw fence so that the blade will take off a minimal amount off of the width of the boards. Then, align the jointed edge against the fence and rip each board accordingly.

Both edges of the boards should now be flat, parallel and square to the faces (assuming, of course, that the faces of the boards are parallel and flat) of the boards.