Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
Preview is mainly meant for photo and PDF viewing. It offers some basic editing tools too.

Basically you could put them on desktop too but get used to the Dock instead. It's much better and easier.

Probably Expose, there is a button for that (F3).
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.