Cabarete is the place to go. You can get there from Puerto Plata on public transportation. Cabarete is one of the best windsurfing locations in the world and lessons are readily available. As you go through Cabarete in the direction away from Puerto Plata, you will come to several shops that rent equipment, give lessons, etc. For anyone wanting to learn windsurfing, this is the place to go.
And don't worry about the rips mentioned in previous post. There are different conditions in different areas. You can be sure that whoever is instructing you is not going to put you in conditions you can't handle at this stage of your learning.