Stop the bloons from escaping by buying things to shoot and pop them!
How To Play Bloons Tower Defense 5
The really simple answer is that you just have to kill those evil bloons. Your task is to guide the monkeys to set up their defense towers in a way that will help them kill all the Balloons that appear on each level. But you have to understand that not all bloons are the same.
Some have very evil features that will try and trick you into believing they are actually harmless. This will be a bad mistake for you to make, and you will learn the hard way.
With a registered account, you will get all the game play for free, but there are a couple of paid features and upgrades if you want to speed things up. These will not be required to get all the tower upgrades, it just means that it may take a little longer.
As you get to more advanced stages you will find that the strategy becomes a lot more complicated and you really have to put a lot of thought and reaction into the game to succeed. This is where it really gets interesting and you will most likely become totally hooked. And all that entertainment comes for free!