You must defend against the invaders of your mushroom farm. Add elements to your towers to gain additional attributes.

Position and upgrade your defenders so that they kill the invaders before they complete the maze.

When you press the Next Wave button you get a bonus added to your cash equal to the number of seconds remaining before the next wave.

The Elements tab next to the Defender tab has elements that you can buy and add to your defenders. Combining elements adds even more attributes.