To gain access to this system, you must first unlock the Automatic Sprite Battle System. A guide for that you can find HERE.
Your Manual Sprite Battle System is now also unlocked. When you reach level 31 and your Sprite has reached level 2 (has a body), Master Nanco in the Sprites' Forest (294 660) has a special quest for you: "L31. Sprite Skill Acquisition". As part of this quest, you will receive your very first Skill Points (2 Novice points)!
You can find the new "Sprite Skills" button in your Sprite Window under "Details". Clicking this button will open your Sprite's Skills window.
Guide by Samurai882