Click on spell buttons, click to place buildings, drag gems to where you need them. Almost everything can be done with the mouse, but there are also some shortcut keys: T - Build tower R - Build trap A - Build amplifier L - Build lightning shrine C - Build charged bolts shrine W - Build wall G - Combine gems B - Throw gem bomb M - Extend mana pool Q - Freeze/unfreeze time N - Send next wave instantly X - Refund mana from gem D - Duplicate gem U - Upgrade (duplicate+combine) gem I - Enable/disable info panels 1,2,3,4,6,7,8,9 - Create gem P or Esc - Go to the Options screen Ctrl-click on a wave stone to send all waves Shift-click on a gem to change target priority