[Ah, the simple yet very important questions newcomers always ask. He almost feels nostalgic.]

You'll find Mareeps on route 32 south of Violet, and using a Pokémon to Surf is indeed possible. But you'll need the badge from Ecruteak, and the HM from Olivine or from a very helpful friend. You can also buy eggs with the necessary type or move from the Breeding Center in both cases, but that'd involve a few additional weeks of training.