When you go into your Black Spirit, click Dark Energy and look on your left, there should be two or three icons on the left side of the screen with LV. xx, depending on your Black Spirit level, it all maxes out on Level 20, except for the third one which maxes out on Level 1.
Those are your Black Spirit skills, they are Rage and Absorb. One is an AOE attack, the other infuses you with a buff. You can read up on them on the Dark Energy menu and clicking on it and looking at the stats and it'll explain what it does briefly.
Hopefully this helps! If you have anymore questions, don't hesitate to ask!