Here is the full list of all 10 Let's Sing achievements.
Play each song at least once
Get 3 stars in 20 songs
Save your diaporama pics
Share a photo on Facebook
Play over 10 songs in one game
Play for 15 minutes
Get 4 stars in one song
Sing a song solo or duo
Play for 30 minutes on a Saturday Night
Get 4 stars in 40 songs