Sorry for the late reply and thanks to taking the time to actually give it a few tries!
We expected that our game was going to be kind of tough to ge into but i'll try to explain how it works a bit better so you can have a better experience! <3
So the gameplay its divided in two phases. The first phase is like the planning phase. In this phase you have to select how many units you want to play to defeat the enemies on top. We always recommend to take advantage of the immunity time at the start of each level to play one unit and then star building a snowball effect slowly playing more and more units.
The second phase starts when you click on the book. Here you will start to play the rhythm mini game, following the patterns of each unit you chose to play, and you start to click on the pentagram or just using the Spacebar (Which i think is easier to play). At the same time that you're playing the rhythm minigame, the combat on the top of the screen also starts to unfold.
Keeping in mind that the amount of units you're going to play will determine how long the combat will be is vital to survive the fight!
Sorry for the long answer, some of this should've been on the tutorial but we didn't have the time to design it that well xD