This book is the shorter preliminary version of Clausewitz's classic On War. It is an OK book, not all that different from Sun Tzu's book by the same title. It has a lot about tactics, strategy, and encampments, and how to organize your cavalry. There is a lot about the minutiae of tactics, formations, territory, and what can and cannot easily be defended. There is also some discussions of troop morale and trusting your officers, and their quality. The book is well peppered with citations of actual battles from which Clausewitz's experience is drawn.
This is probably the first modern book on war, but it is not the last word. There are some good pieces of advice/wisdom interspersed throughout. "Victory is purchased by blood", "a powerful emotion must stimulate the ability of a powerful military leader", "We may be sure that an army will never be in the condition supposed by someone following its operations in an armchair", "have faith in our own insight and convictions". . . are just a few of the little pieces of advice he has for the aspiring military leader.
All in all an interesting read.