How to make an adrenaline meter to execute special moves in unity?

Hi! I want to make a secondary meter that will let me add special moves to my game. It will fill up as i defeat more and more enemies. Is it possible to do that? Can anyone help me?

 

Or I could make it fill up with collectibles.

 

Try starting here: https://unity3d.com/learn

and work your way up.

 

It would work the exact same way as a health bar but in reverse whereby you increase the bar rather than decrease it, as for the special abilities themselves, you activate them with an if statement that detects a keypress and so on if your 'adrenaline' integer is high enough. Anything to do with progress bars and so on is purely cosmetic most of the time.