In the first room, just wait or jump around a bit (wasd) - you will encounter a demon in a few seconds.. In the fighting room, click the attack or fireball button then click where you want to shoot, if you click the heal button you should click the player after, but you can also heal the demon! You can pause the game in any level, but pausing during a fight will bring you back to the first level.
WASD
CLICK
P