The Triduum celebrations begin on Holy Thursday or Maundy Thursday (from the word mandatum) with the Mass of the Lord's Supper in the evening.

This day commemorates
* the great mandatum or call to service
   John 13:1-20
   The mandatum of Jesus is his command to follow his example (Jesus washes the feet of the
   disciples), to do as he has done.

* the institution of the eucharist
   Matthew 26:26-30, Mark 14:22-26, Luke 22:14-23
   Jesus institutes the Eucharist, giving his body and blood to his disciples. As we share the
   consecrated bread and wine, we experience the fullness of Jesus' gift to us of himself. It is
   important, especially on this night, to receive the host and the cup, in memory of Jesus.

* the prayer of Jesus in the garden of Gethsemane
    Matthew 26:36-46, Mark 14:32-42, Luke 22:39-46
    After the meal with his disciples, Jesus went to the Garden of Gethsemane to pray. "Could
    you not watch one hour with me?" he asks his disciples as they fall asleep on him. Adoration
    of the Blessed Sacrament takes place until midnight when we keep Jesus company.

There is no final blessing or procession to end this Mass because the celebration does not end.
The prayer continues in our homes until we are called together again on Good Friday to remember the next part of the story of our salvation.