Quite often we see Catholics (novus ordo AND traditional) who argue that we don't worship Mary but rather give reverence to her. This is mostly to argue against protestants who call us idolators. But, the fact is, we DO worship Mary. The problem is - what sort of worship is forbidden by the first commandment? Here is the answer:
Latria: this is the form of worship which is highest - it is adoration and is given to God alone. To offer latria to anything but God is a sin against the first commandment. This is what we do when we bow down before the blessed sacrament.
Hyperdulia: this is the second highest form of worship and it is given to Our Lady only. It is the special reverence we hold for her as the highest of saints.
Dulia: this is the form of worship given to the saints, statues, icons, and humans (by humans I mean the worship given to a King, etc). Dulia is veneration due to excellence of a created being.
So all three things are worship - we do worship Our Lady, we do worship the saints and angels, we do worship rightful Kings, but we only worship God with adoration due to Him alone. To offer the type of adoration we must give God to a created thing is idolatry.