Press the arrow on the right side of the screen to open the shop menu Purchase towers to hold off the enemy Upgrade towers buy clicking on them and pressing the upgrade button that pops up Enemy info cards pop up the first time you meet and enemy, click on them to remove them (you can only remove the one at the top) There are currently 5 towers and a bunch of enemies First 25 waves consist of Zombies and after that you will be attacked by Aliens
Thanks to warfame for tower defense tutorial