We bought a boat.. albeit a small one, asked a friend to spend a weekend helping us deliver it home and do some basic coaching, and figured it out from there on our own. Of course 30 years and 5 boats later we're still learning.
The courses will help, obviously, but there's lots of publications and 'how-to's available and it is possible to 'teach yourself' through experience. Depends mostly on a 'can-do' attitude and some basic common sense approaches.
If your area has a local chapter of the Power and Sail Squadron, their introductory courses are very good from a basic boating point of view.. reading charts, learning navaids etc.. lots of subjects that, while not sailing theory specific, may well save you from driving that 'new' boat onto a sandbar leaving or entering the harbour. I'd recommend them as starters.
But I don't think it's strictly necessary to take 'all' the courses first.
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)