You do everything with the left mouse button, the game is a menu driven RPG.

In battle, once you do three attacks, you will have enough BP (Belief Points) to do a special attack. You will unlock more special attacks as you explore and find items.

As a warning, once you leave a floor there is no way back. Make sure you find everything you think you'll need before going forward.

If you fall in battle, your partner will revert time for you, allowing you to try again.