Start the wave to start spawning the enemies. Place turrets to defeat the enemies. Defeat enemies to get more money. Upgrade your turrets to give them better stats, For example: Better range or Faster firing speed. Turrets: Basic, Shoots really slow and just sucks. Rare, The exact same as Basic but it shoots faster. Epic, When an enemy is in it's range it will charge up and give you five bucks each time. Legendary, Charges up and then shoots a laser (It's OP).
Thanks to warfame for the awesome tutorials on how to make Tower Defense! Check him out here: https://scratch.mit.edu/users/warfame/