While at the Vatican's official website, you can look at a catechism. Among many other things, this catechism addresses what the Roman Catholic Church believes and teaches about Mary. Read it by clicking here.
There are several things that I find very troublesome. I'll quote a few of them below:
964 - "This union of the mother with the Son in the work of salvation..."
966 - "Finally the Immaculate Virgin, preserved free from all stain of original sin, when the course of her earthly life was finished, was taken up body and soul into heavenly glory, and exalted by the Lord as Queen over all things..."
968 - "In a wholly singular way she cooperated by her obedience, faith, hope, and burning charity in the Savior's work of restoring supernatural life to souls. For this reason she is a mother to us in the order of grace."
969 - "This motherhood of Mary in the order of grace continues uninterruptedly from the consent which she loyally gave at the Annunciation and which she sustained without wavering beneath the cross, until the eternal fulfillment of all the elect. Taken up to heaven she did not lay aside this saving office but by her manifold intercession continues to bring us the gifts of eternal salvation .... Therefore the Blessed Virgin is invoked in the Church under the titles of Advocate, Helper, Benefactress, and Mediatrix."
971 - "The Church rightly honors the Blessed Virgin with special devotion. From the most ancient times the Blessed Virgin has been honored with the title of 'Mother of God,' to whose protection the faithful fly in all their dangers and needs..."
If you believe that church tradition holds authority in life, then the above statements probably cause you no concern. However, if you hold to sola scriptura, then the above statements about Mary ought to cause you to cringe. The reason is simple: the statements cannot be supported scripturally in any way.
This is not a small issue. Rather, statements like what we see above are a frontal assault on the gospel itself. The gospel is all about the work of Christ. We are nowhere told to worship or venerate any other. God is a jealous God who alone deserves the glory. Christ alone is our Mediator. Christ alone was free from sin. Christ alone is our King. Christ alone ascended into heaven.
If we are to be biblical people, we must reject Roman Catholic teachings about Mary.