How do I use dual displays to have a full screen app on one monitor and another full screen app or the desktop on the other?

How do I use dual displays to have a full screen app on one monitor and another full screen app or the desktop on the other?

I want to have my itunes visualizer on my TV which is connected via HDMI adapter, and still have access to full screen itunes and my desktop on the main display.

Any suggestions? App downloads that can do this? Please let me know.