My experience with the Win8 preview looks ok. click on something, which launches an app. cool, but now how do I get back. spent probably 10 minuted getting in

My experience with the Win8 preview looks ok. click on something, which launches an app. cool, but now how do I get back. spent probably 10 minuted getting increasingly frustrated at not being able to exit back to the home screen (or whatever it's called. it's obviously not the desktop, because there's a tile called "desktop" that should be called "normal windows"). In the end I gave up and gave it to my wife, who did manage to figure it out (hint: you have to move the mouse to the very bottom left hand pixel) Also - it appears I'm unable to use the email client at all unless I sign up for a live account. What's up with this?