First you want to make a new folder, be sure to put it anywhere on your computer that you can locate on the editor later.

I like to put mine on Documents, its a personal preference!
Open the newly created folder, and put the song file on it. As of right now, the editor only supports an MP3 and OGG file.
Rename the song file to : base.### (### is mp3 or ogg depending on the original file extension)
If there’s no .mp3 or .ogg at the end of the song file name : Move your mouse on the “View” → Press “Show” → Press “File Name Extensions”

Once you’re done, you can now open the editor and press “Open Folder”

Locate the folder you just made before, and press Select Folder

And you’re now able to hear the audio! You can press “Space” to Play/Pause it.