turbo????nos??? what?

What exactly does a turbo do? I know it has somthing to do with compressed air and the exaust system. Iwould also like to know about what exactly nos or nitrous oxide does.

http://auto.howstuffworks.com/turbo.htm

http://www.holley.com/nosnitrous/index.html

http://auto.howstuffworks.com/framed.htm?parent=question259.htm&url=http://www.idavette.net/hib/nitrous.htm