To Use hero - move it near enemies, so He will shoot them down. Hero shoots in auto-mode.
Build towers from the same group to raise a total damage. Each group of towers increases something special for all groups.
WASD/Arrows for moving hero, 1-9/Mouse_wheel - changing weapons, P - Pause, Space - highlight hero.
-/+ - changing speed of game, Holding Shift - makes game faster.
If game is to tall or to wide - just use F11(fullscreen).