Drives just like a car, which is not surprising since the boat mod’s basically hacked on top of the current vehicle code. You sit on the tile with the oars, press ^, and away you go. Well, provided you’ve got enough of the boat sitting in water tiles.
Just watch out for schools of fish, they don’t go under your boat as-is, you ram into them and damage your boat. I find it helps to zig-zag in areas with lots of fish, it gives them a chance to get out of the way. Oh and beware of Jawed Terrors, their name isn’t fanciful. I’d bring a shotgun along just in case.