How do I Spend Skill Points
Every time you level up, you can gain 1 skill point which can be applied to a skill in the skill panel to improve the skill.
Some skill cannot be improved by skill point unless some certain skill has been improved by certain skill points. Some skill cannot be improved unless the player reaches a certain level.
Unactivated Skill: Such skill cannot be activated unless some certain skill has been improved to a certain degree. See the image below:
Active Skill: Such skill can be improved directly by skill points. See the image below: