Hi,
Yes the save as will save the project in Audacity format so you can continue working on it at a later time.
You want to save the audio it's EXPORT AS..and choose either Wav or Mp3. Both of these are audio formats recognised by most computers. As I said before if you don't already have the Lame 3 codecs you will need to install these first before Audacity will save in mp3 format. There is a link to where you can download these from
http://audacity.sourceforge.net/help/faq?s=ins tall&item=lame-mp3
If you need to play the resulting files on an audio system you will need a further conversion process usually handled by Nero and other cd burning software. For this you need to choose create an audio cd from the starting menu and follow the on screen instructions. Mostly it's a very easy drag n drop system to add the audio files one at a time.