Helppppppppp meeeeeeeeee!!!
On the sound behavior block, there is a text box that allows you to paste/type the URL of a website that plays the song/music. HOWEVER, that URL must have “.mp3” at the end, otherwise it won’t work. Be sure to ask for permission from the artist to use the song in your game if the song is copyrighted. Otherwise, you might get sued or face other legal consequences.
Oh thanks a lot @Superstargames