Basically the similar games you get outside. Go through 3 stages with your 5 characters. Multiple ways to upgrade them. Level up. Skill up. Skins. If you want to raid stages you need to spend some money just buy anything and you will be able to raid stages.
Daily quest. Get exp and money and other things. Claim energy at certain times of day
There is also a bunch of things you can do in the guild. Like summoning titans. Level up titans.