There is some info regarding keys and such in the game page. I'll reiterate them here. Tab toggles whether the mouse is locked or now (at well as hidden), Escape exits the game (no menu yet) WASD or Up Down Left and Right arrows to move, Mouse to turn camera. Left Mouse to shoot, fairly standard stuff. You lower your gun when pointing near an enemy, and in this state you can't fire.
This game got plagued with some bugs and difficulties early and late on, resulting in some major scaling back and simplification of the game, so sorry it's not more fluid. I'd have loved to have spent way more time on Animation and some enemy AI problems made the simpler tasks take longer than they should have, as a result the game is very simple, very small and very short.