Assuming you are talking about a woodworking miter saw:
A miter saw is a handy tool for cutting angles in wood. To rip wood with a miter saw, set the blade to 90 degrees and make sure the fence is flush with the side of the blade. Then, adjust the depth of the blade so that it's just barely touching the wood. Next, slowly feed the wood into the blade, keeping your hands close to the fence so that you can guide it through evenly. Finally, turn off the saw and let it cool down before removing your piece of ripped wood.