If you have the caliper in your hand you've already taken the pins out, clean those pins good and replace them if possible. Now clean off the piston face that touches the inner pad(round) and the face that touches the outer pad. Its on the other side of the caliper.
You will see that the bracket thats still bolted on has small lands that the caliper slides in and out on as the brakes are applied and released, sand them also then clean all the surfaces you just sanded with brake cleaner. Now you must push the caliper piston back in. Since you don't do this kind of work all the time it might be best to use a large pair of water pump pliers called slip joint pliers, the bigger the better. You could use a large vise grips that are usually used for welding it is c shaped. A C-clamp works good also, a big one. After its pushed in completly you can push the inner pad into the caliper, remember to peel the paper off the sticky surface or use the anti-squeal on this part of the pad that contacts the piston. Be sure you place the anti-squeal clips onto the new pads if they do not have them on already. Then apply the goo to the outer pad or peel the paper off the back of the outer pad. Do not allow any of the anti-squeal to contact the braking surface of the pads. Now you can install the outer pad on the bracket, slide it on from the inside. Then place the caliper with the pad snapped on it into the bracket. Now start the two pins. After you tighten these pins and the clips are in place spray any grease or oil off any braking surface, use the can of brake clean. Thats it, remember you will not have any pedal for the first few trys, so be careful, I almost drove into many a wall as I would frantically try to get a pedal when I pulled the car back. Ok? The clips are anti-rattle clips, they are just for noise. They just work like a spring to hold tension on the two pads.
Good luck and be careful.