The light switch has 2 screws on the side and 2 holes in the back, what's the difference? I have power coming from one set of wires, then I have another set going to the light, how do I hook up the swich?

You have the option of connecting to the screws or "back stabbing " into the holes. How was the original switch hooked up? Normally, the hot black goes to one screw and the other black goes to the other screw, whites are wire nutted together. Older switches did not have a ground screw. I don't like to use the back holes but it is an option .