The function you're looking for is located in Music Maker's "File" menu. Just look for the "Export arrangement" option. This will enable you to mix down your songs and output them into a standardized audio file format, like WAV, MP3, WMA and OGG Vorbis. This way, you won't actually need Music Maker to replay the songs again. You can pass them on, upload them to websites and people can just replay them using common programs like Windows Media Player, WinAmp or VLC player.
I've never uploaded a song to Facebook and I'm not sure what formats are accepted. I suppose you'd be using a special Facebook widget as the actual player/jukebox. However, it's pretty safe to say that such a widget would probably support most or all of the formats mentioned above.