tip hold the bottom of your steering wheel and turn your hand in the direction you want the tailer to go.
Try practicing in empty parking lot if you can.
If you think backing up with the boat on is hard, wait until you try backing just the trailer alone. maybe on flat ground you can see it, but once the trailer starts down the ramp, you lose sight of it. Hard to do, but the only way to see it, is with the side mirrors.
Good luck and enjoy.