Okay, first of course you have the music in .ogg format
let's call it 'this_is_my_music.ogg'
put this ogg file into the sound folder
then have something like this in your description.ext:
class CfgMusic
{
   track[]= { my music };
  Â
   class mymusic {
   name = "mymusic";
   sound[] = {"this_is_my_music.ogg", db+0, 1.0};
   };
db+0: use -x or +x to in- or decrease volume
you can now use the playmusic command followed by the class name (or name not sure)
in this case you would use: playmusic "mymusic";
might be other ways but this works for me, hope it helps
MadFred