Airport Express

I'm a lil confused....can someone explain how you can stream music wirelessly to any room in the house and how you get it to play on other stereos?? using AirPort Express

After setting-up your wireless network to see the Airport Express unit. You simply plug the Airport Express into a wall outlet... Then plug your powered speakers into the the Airports Express. Within iTunes, on the lower right side of the window there is an option to choose "Computer"... you click that, and you're given the choice to play the music through the Computer, or any Airport express unit, or Multiple.

I have mine labeled "Computer" "Upstairs" and "Downstairs". I use it daily. works perfectly.