A combat training book is given to the player by Markus, who is standing just outside the entrance to the Slayer Tower. To receive the book, the player will have to talk to Markus after completing a Slayer contract and select the option to receive an amount of combat experience.
It can award 156 to 28,000 experience, depending on which Slayer contract the player has completed. The higher the Slayer level and amount of creatures a contract contains, the more XP is rewarded. The player can choose which skill will obtain the experience, choosing between Attack, Strength, Defence, Ranged, Magic or Constitution.
It can't be used on a skill if the awarded experience is more than 10% of the skill's current experience. For example, a combat training book which gives 12,852 experience must be used on a skill with at least 128,520 current experience. When attempting to do so the message:
"You can't assign the XP to that skill because it's more than 10% of the XP you already have in that skill. Try [Skill name]" will appear.