Hi, Angie. The fix is probably a lot easier than you think it is. First, are you talking about a drip from the faucet or water showing up around the trim ring, or a leak behind the wall. With these potential areas, it will be difficult to cover all of them so we really need a lot more info if we are going to make it an easy answer.
Even if it is a leak behind the wall, the water can be coming from somewhere else, like the shower head or the piping that goes to it. Do you have a small door behind the faucet so you can see what is going on there?
Can you give us some idea of your level of do-it-yourself knowledge and experience so we can try not to talk too far over or under your level. If you are a novice, no problem. We all had to start somewhere and here's some basic info to get us started. www.doityourself.com/plumbing/faucetbasics-e2diy0257.htm This shows a sink faucet but the layout for a bath faucet is the same, just turned on the side.