I agree that I didn't give enough instructions for new players. I personally love games that don't give many instructions and leave most of the game for players to explore (like Rain World), but that's probably not a good design for such a short game like this.
If you want to jump for the max amount of height, you should attack and jump at the same time. The light attack can only hurt dark enemies and the dark attack can only hurt light enemies. You'll know that they got hurt when you see them being pushed/pulled by your attacks.
Also, the pulling force given by the dark attack is depending on the distance between you and walls. The closer you are to the walls, the stronger the pull is. Another hidden fact is that your horizontal movement speed doesn't go down, even when you are on the ground, as long as you are holding the movement key with the same direction you are moving. This allow you to skip some areas if you are good enough.
I'll probably add these information in the description later.