Welcome
I ususally get crabs at driftwood island. To board a ship you need to hit it with your grappling hook. You aim at the green circles and select grappling hook when using your cannon. Once you get several hooks on the ship it'll tow the ship closer to you and asks if you want to board.
lol If you're loney in the game send me a pm and let me know when you're on, I can help you