If the game freezes, just click inside it (games can get unresponsive if you click elsewhere on the page).
Protect the tower from the bombs with the help of shield. Move the shield up and down to prevent the bombs and get more score. Achieve the target score before the time runs out and move onto successive levels. Each missed bomb may causes damage to your tower and also reduces your obtained score. More damage causes fall off the tower and your game will get over.
This game is played with mouse only.