Place towers in their appropriate locations. Some locations any tower can be placed and others offer bonus' like increased distance or mana generation. Pass each mission by not allowing all of your gem's to be stolen.
Cursed Treasure is very different from many other tower defense game. Instead of not letting enemies get to the end of the maze your goal is to save at least one piece of treasure (gems) for all the waves you have to pass. One other twist is you can only place certain towers in certain locations.