If you have a single lever faucet, you probably will have to disassemble the faucet. But shut off the water before you attempt it.
There are 3 types of faucets, compression, rotating ball, and cartridge.
If you have 2 handles, its generally a compression, or a cartridge. You can easily fix them. One of the easiest ways is to pick up a book by Black and Decker on Home plumbing repair. You will then be able to follow a step by step proceedure for repair.