The Triduum is the 3 days preceding Easter: Holy Thursday, Good Friday, and Holy Saturday.
On Holy Thursday we commemorate the Last Supper; the beginning of the Eucharist. Washing of feet is also done: “So when he had washed their feet / ...he said to them, “Do you realize what I have done for you? / ... I have given you a model to follow, / so that as I have done for you, you should also do.” (Jn 13:12, 15) Mass is celebrated in the evening because Passover begins at sundown. No masses will be celebrated until the Easter Vigil on Holy Saturday. This was very emotional last night: The altar was stripped, and the tabernacle was opened. Seeing that empty tabernacle was heart wrenching.
Good Friday: The day when Jesus died. The day when the world realized that they crucified the Son of God. Upon walking into the church, one sees a bare altar, with the tabernacle that holds the monstrance (which holds a suspended host) open, but empty.
On Holy Saturday there is an Easter Vigil in which Catechumens are received into the Church. These new members have gone through RCIA (the Rite of Christian Initiation for Adults), have studied the Catholic Faith, and are ready to become full-fledged Catholics. I've never been to that Mass, but I've heard it's incredibly long. And beautiful. The Mass begins in darkness; the Easter/Paschal Candle is blessed and lit.
After the Catechumens are baptized into the Catholic Faith, the veils come off of the statues on the altar, bells ring, and the "Gloria" and "Alleluias" return. It's officially Easter!
Resurrection Cookies are a really neat way to take part in the Easter Story with kids. You can find the "recipe" here.