The goal of the core experience is to reach the exit without getting caught. Press WASD to move, C to crouch, and F to interact with objects. The second mode adds guns into the mix. Hold RMB to aim down sights and click LMB to attack. Keep in mind that normal bullets are not enough to kill a supernatural being. To banish the abomination for good, find 6 crosses hidden somewhere on the premises. Until then, search the classrooms for ammunition and do whatever it takes to stay alive.