When you go into an app make sure you hit the trackwheel and choose close.
I know how to hit alt and back key to see them, but now that I see the how do I close them
Do they have an app that can show realtime what is running in the background?
Emanipate Yourself From Mental Slavery, None But Ourselves Can Free Our Minds... (Robert Nesta Marley)
you can try alt-backspace key
FYI you can't close all applications. There are several that always run in the background.