One of the 2 main things that distinguishes Catholics from other Christian denominations, is our belief in the Real Presence of Jesus Christ in the Eucharist (Blessed Sacrament/Holy Communion).
We believe that at the Last Supper, Jesus instituted the Eucarist as the Holy Sacrifice of His Body and His Blood. We believe that when the priest says the words, "This is My Body...This is My Blood," during Holy Mass, through Transubstantiation, the bread and the wine, while still looking and tasting like bread and wine, are changed in their very substance, to The Real Body and Blood of Jesus.
Throughout the Scriptures, we can see as well that Jesus Instituted the other 6 Sacraments as well. We believe that all 7 Sacraments were instituted by Jesus as His way of showing us His love for us and His lasting Presence with us in this life!