There are instructions on the main menu
Bumper soldier (Bottom right) 5 cost 10 seconds till created Indestructible little guy. (He grows)
Kamikaze (Left ones) 10 cost 7 seconds till created Touched an enemy? Let's blow up. (He also grows)
Tailed warrior (Top right) 20 cost 30 seconds till created Self-explanatory (Starts off big, does not grow.)
When you lose, there will be a score. The longer you survive, the bigger the score!