Have you been asked this question by non-Catholic family and friends or by Jehovah's witnesses who knock on your door?
This is how you can respond.
Catholics do not worship Mary. We love her and honor her as the Mother of Our Lord Jesus Christ. We love her as we love our own mother here on earth and are devout to her for her saying Yes to God when the Angel Gabriel appeared to her.
The Hail Mary prayer is from scripture:
Luke 1: 28 - Hail Mary Full of Grace The Lord is With Thee.
Luke 1:42 - Most blessed are you among women, and blessed is the fruit of your womb.
Also we see Luke 1: 48 Mary proclaims - All generations will call me Blessed. As Catholics we live these scripture verses.
To summarize Catholics do not worship Mary. We love and honor her. She is our Mother in heaven and Mother for the Motherless. Mother of Jesus Christ our Lord and Savior. She helps us on our journey in life through Christ our Lord.