【SAMURAI WARRIORS 5/PS4】 How to use "Principles of War" and "Strategic Tome" purchased at a Shop

The values of "Stock Weapon Mastery" in "Principles of War" and "Skill Points" in "Strategic Tome" are added at the point of purchase.
"Stock Weapon Mastery" and "Skill Points" can be used from [My Castle] screen > [Dojo].