You need to cut two slots for your miter gauge. They should be equidistant from the upright blade on both sides of it. The slots should fit the bar of steel you use for your miter gauge so that it slides easily, but without looseness. The two slots must be exactly parallel to one another.
If you can borrow a friend's table saw, cutting slots for the miter gauge is easier, especially if he owns a dado blade attachment. An alternative method is shown in the next steps.