The aim of the game is to control the number of monsters in the maze at any one time by building towers which can stop them. To build a tower, simply click on its icon on the right of the screen then place it on the map by clicking again. Towers can only be built on the raised ground around the paths. All towers can be upgraded to improve their strengths, to do this click on the tower then click on the upgrade button which appears on the right. You can also sell towers to make back some extra money. How many levels can you last? Target low health monsters by clicking them as they walk on the path. All towers in range of that creep will focus fire to try and take it out quicker.