Christianity: Emphasis on "everyone is a priest", equality between people. The authority of faith is: "Scripture Alone" (Sola Scriptura)
Catholicism: Strict hierarchy: Pope → Bishop → Priest → Laymen. The authority of faith is: Bible + Church tradition + Church decree.
Christianity: Justification by faith, salvation by faith. The only sacraments are: Baptism and Eucharist.
Catholicism: Faith + good deeds + sacraments (such as baptism, Mass) can be saved. Seven sacraments (baptism, confirmation, Eucharist, confession, marriage, holy orders, anointing of the sick).
Christianity: Mary is only the mother of Jesus, and does not accept prayers. Saints are not worshipped, only Jesus is the mediator.
Catholicism: The Virgin Mary is revered as "Mother Mary, Intercessor", and prayers are prayed to her. It is also allowed to ask saints for intercession.
Christian Church: Emphasis on preaching.
Catholic Church: Emphasis on mystery, solemnity, and ritual.