I'm not sure if your question is how to add music to your game, or where to get music from. But I think you mean the last.
There is no specific software that you need to use, if you want to compose your own music. It's just important that you have a sound file as a result that is supported by AM.
To be honest, I don't compose the music myself, so I can't recommend you any good software for that, maybe another member can.
I usually use pre-made music that is royalty free (you need to pay attention that you don' use copyrighted music without the agreement of the licence holder).
In this thread you find also links to royalty free music:
http://www.adventuremaker.com/phpBB2/vi ... php?t=1262
But it's rather expensive. However, there are some sites that have also some free loops or even music to download, just use google. In addition, some independent composers allow you to use some of their music files for free, or sell it very cheap. They can also be found using google.