How to make a power bar with button for mobile games in unity 2d

Hello everyone,I don´t have any idea about how to make a button with powerbar for mobile games in Unity 2D, this button needs to have some relation with the power bar and the powerbar needs to apear in the screen.
When I press the Button the Powerbar needs to go Up and When I not press the button the powerbar goes down.

Example the Mortal Kombat test your might:

Someone have any idea how to make this?
i´m a beginner in unity, but a make some tutorials at the site and I using Unity 4.6.
Thanks for all.

Google is your friend, plenty of people use progress bars(power bar) for all sorts of things.

Here is a tutorial with 4.6 and the new UI components, just make it vertical instead of horizontal.