Jesus and his disciples went to a certain upper room (that happened to be not very far from Jesus' mother's apartment), and there they shared the Passover meal together, and inconceivably more.
As the Passover made each generation of Israel actually present in the exodus from Egypt, so the Eucharist makes us truly present at the Lord's one Sacrifice through all the ages. Remember that it is the evil child who says, "The LORD brought our ancestors out of Egypt." Note, not himself, just his great-great-grands. We are as much present, as much implicated, as our ancestors in the first century AD.
And we believe that it was in this night when the Lord Jesus instituted His first priests in the new covenant, saying to them, "This is My Body... this is My Blood of the new everlasting covenant..... do this in memory of me." [anamnesis, we still call it, it means "to not forget"] Now, of course, this doesn't mean priests are perfect. Even the first ones, Jesus' Twelve, weren't such a great lot. One would sell Jesus for 30 silver pieces before the night was over. Nine others would scamper away like a bunch of scared mice. Another, before morning dawned, would deny repeatedly ever having known Jesus. Yet, they were the ones chosen by our Lord.
[Pray for priests!]