By getting a boat. Getting on someone else's boat is good too, as you can get experience and learn from them. Sailing is easy - you don't need to win races when cruising around the world, so the finer details of trimming will be wasted on cruisers (you can always pick them up on the way). Navigation and traffic rules shouldn't be hard to pick up for the average HN crowd, although yachties like to make a fuss about it.

I did a few RYA training things that cost a lot of money and got me some papers that nobody ever wanted to see (they're important if you want to charter a boat though). You can just buy the syllabus and gain the knowledge by online learning or video courses instead. I recommend going that route - the knowledge in the syllabus is important and very useful. The formal course in a classroom and the certificate are not. Practical knowledge is gained only by going sailing, making mistakes and learning from them, but it helps if you know the knots and the parts of the rigging beforehand.

But the real learning only begins when you get your own boat and have to fit it out and keep it going. Boat maintenance is hard and there's a lot to learn. You can initially substitute money, but that stops working once you get to remote areas where there is simply nobody else to pay to fix your boat and you will have to do it yourself or give up. Many decrepit boats in remote locations are on the market very cheaply for exactly that reason.