Then he took the bread, said the blessing, broke it, and gave it to them, saying, "This is my body, which will be given for you; do this in memory of me." And likewise the cup, after they had eaten, saying, "This cup is the new covenant in my blood, which will be shed for you."

- Luke 22:19-20

As Catholics, we believe the Eucharist is the Real Presence of Jesus Christ. In Consecration, through the hands of a priest and the grace of God, bread and wine are really and truly transubstantiated - transformed in substance -  into the body and blood of Christ. 

Christ initiated the Eucharist at the Last Supper, the night before He was crucified.