I need help on photoshop. Let's say I have a square:

and a circle:

I want to put the circle on the square and cut out everything around the circle, leaving a blue circle. How is this possible?
And don't say "Draw a circle on the square and cut it out", 'cause that's not what I need. I need this to work with any kind of shape, such as a bird, and I want a blue bird out of the blue square.