It takes place during and after season 1, where after the baby is born, Quinn leaves her with Finn and runs away to California, I think. Puck follows her, so Finn is left to raise the baby. Kurt helps him, and they eventually get together.
They call the baby Melody, and she calls Kurt Mama.
There's a sequel that takes place about a year later where Quinn and Puck come back to see Melody and though Kurt worries that they'll take her away, Puck promises that they won't.
FOUND! Link in comments.