What is the song Mamma Mia by Abba about?

"Mamma Mia" tells the story of a young woman on the eve of her wedding, Sophie, who is trying to figure out who her father is. She finds three potential candidates, and decides to invite them all to her wedding in the hope of finding out the truth. The ABBA song is a light-hearted and cheerful tune that captures the excitement and uncertainty of the situation.