In order to understand the forces on a boat, practise experimenting with them. Rudderless sailing is one of the best exercises in assisting you to understand this, but make sure you practice with lots of room around you! See chapter 1 (Seamanship Skills) of this book.
Once you have mastered sailing on a beam reach, try sailing around a triangular course using all the points of sailing. This chapter is about understanding the forces on the boat – how to use them in light winds and neutralise them in strong winds.