You can't learn anything without doing a practical and all the sports need basic training and learning, but before jumping from the plane for jet skiing, going on the field or in the water you have to learn its knowledge, history, ways, techniques, skills, etc and that stuff you can find in books, I've read a book about skiing, it's very good about skiing and it's called Surf Ski Supremacy, it has all about paddling, controlling balance, how to stay on the board, how to become one with the ski and the ocean and much more.
