Desktop: WASD move, mouse aim, click to shoot, Shift sprint, R reload, Q / 1-4 swap gun, G or Space grenade, Esc pause. Phone: drag on the left to walk, drag on the right to look, hold FIRE.
Survive the horde. Kills give XP; every level lets you pick an upgrade, and every upgrade has a trade-off. New guns unlock at levels 3, 6 and 10. Headshots can kill outright. The Abomination comes at 3:00. Red barrels explode.