Check out how a sump works
for more info on what they are and do.
You need to get quality test kits for pH, ammonia, nitrite and nitrate to start. A phospate kit would be nice too, but you can probably have your lfs
test your source water for that.
Read the articles on this site and then post more questions about what you are thinking about buying. You'll usually get good feedback about a product's quality.