When talking about a directory, the "/" symbol represents the root of your mod. So for example, for me, it is "C:\Program Files (x86)\Steam\steamapps\common\Starbound\mods\musicMod\"

First of all, create a new folder in your mods/ folder, and call it "musicMod"

Then, follow the instructions from the "HOW TO : COMPATIBILITY OF YOUR MOD" topic.

Once it's done, you should have a file called "/datafiles/jukecrate/DIRECTORY.json"

Now, add your musics to the "/music" repertory
WARNING : Your musics must be in .ogg format. Look on the internet about how to convert your musics to the .ogg format

And add a block as explained in the "HOW TO : COMPATIBILITY OF YOUR MOD" topic for each of your musics.

Finally, go to the root of your mod, and add a _metadata file
WARNING : It must be _metadata, and not _metadata.txt . By default, Windows hides the extension of your files, so when you create a file, it automatically adds the extension at the end ! Check on the internet about how to disable this

In the _metadata file, add this code block :
You can change anything except the steamContentId, the link, and the requires array.

Et voilà.