If you're wanting to put new music, you basically move the music files you want into FeralHeart>Media>Music.
Then you open your "music.cfg" file and in it, you'll see something like this:
[Title]
media/music/Title.mp3
And so on. The name in the brackets is what map that music plays in. So if you want your song in a certain part of the map, say....you want a certain song to play in The Grounds, it'll go like this:
[Plains]
media/music/Songname.mp3
Keep in mind, that will make the songs play in maps that aren't in caves. Same goes with caves too. If you want a certain song to play in cave maps, it'll be like this:
[Caves]
media/music/Songname.mp3
And make sure your music file is in .mp3 format.