You can buy your very own boat(s) at the blue sail boat icon on the map at postal 356. If you want a more high end boat, there’s a couple of fancier boats available from the yacht salesman at postal 348, the tan colored yacht icon.
You can get your boats out of the garages at the blue boathouse & anchor icons.
Same laws as other vehicles are in effect. Like no drinking and boating, no dangerous boating, etc.