For the People that do not know how to encounter the different tasks in this game:
In case you didnt read it carefully, the bow is equipped by holding the SHIFT button.
The Catapult does not need to be attacked or defeated, just stay as close to the right border of the screen as possible it cant attack you there, you will have won the lvl when youve slain all the enemies.
The last boss can only be attacked mid-air, target his legs/feet so he will jump, then target him with your sword while hes jumping, hit him a few times and he will be dead.
+ this so people can read it :)
You can hover the DPS number in the top left of the screen, and it shows you a rough breakdown of what each Champion is contributing to your DPS.