This game is opposite to Tower Defense games. You dont build towers, but create units that need to reach the exit passing through enemy towers. So you send waves of monsters instead of defending against them. Use YOUR MOUSE to choose the entrance and rotate junction arrows to define the path your units will move along the path and try to make the required number of units reach the exit alive. You can select from various unit types and versions. Click "Let it Out" button to send your units. Good luck!