Alright, so, can somebody help me with a couple of questions I have regarding fleets? Like, naval fleets?

I'm trying to design a naval/space fleet in a fantasy/sci-fi universe, basically, for a Snake Goddess character I have. I'm trying to decide how many ships it should possess, and of which types, but I'm having difficulty researching what different types of ships do.

Can someone give me quick, concise descriptions for the purposes and features of different types of ships, such as Corvettes, Destroyers, Frigates, etc.? It'd help me a ton.

I'm posting this in a few different boards. Unsure which is best for this.