In today's liturgy we celebrate the birth of Mary. There are only three birthdays celebrated in the liturgy: those of Jesus, Mary, and St. John the Baptist. Usually, the Church celebrates a saint's feast on the day of death, because that's when they entered eternal life.
But Jesus, Mary, and John the Baptist played very important roles in the history of salvation, so their lives on earth were extremely crucial for all of us.
We don't have historical records about Mary's birth. The names of her parents, Joachim and Anne, come from an ancient document called the Protoevangelium of James. It is not a canonical Gospel, so we can't rely on it for historical details. But it was an important source for the development of Marian piety. It was written in the early second century, and shows that, among other things, Christians in that early time believed in Mary's virginity.
Like us, Mary lived a human life on earth. It was hard. She had to struggle, even though she was graced from the first moment of her conception and never sinned. She dealt with suffering and sorrow. But on her birthday, we can celebrate her life as one of us, our spiritual mother, our friend, someone we can always go to for help.