FIrst, you need to import a sound in your project. After you’ve done that, you have two options on how to use your sound:

-- As a parallel process (the sound plays at the same time everything else is happening); or 

-- “consecutively": first plays the sound and then the other action will begin.

Both examples assume you have both imported a sound called my_song and created a Dance procedure.

Parallel Process example

If you run 

launch [my_song] Dance

-- the sound starts and the turtle starts dancing at the same time.

Consecutively example

If you run

my_song Dance 

— first, the song plays completely and then the turtle starts dancing 

In case your song is too short so you want it to keep repeating, use

forever [my_song] Dance

in this case, the song will repeat forever, until you stop it by pressing the Stop All button.