The following theoretical knowledge, among other, is covered in the sailing courses:
If you want to learn sailing, you need to get out on the water, feel the forces working on the boat , You need to put in many hours of practice to master it.
Theoretical knowledge is also important, and gives you a better understanding of sailing.
You can learn a lot of knowledge in advance, on shore.
Being on the water you can then focus 100% on sailing itself. Knowledge of theory beforehand is not necessary, but will certainly speed up your learning process during the course.