Tonight begins the Easter Triduum, which is basically the most intense period in the liturgical year. The Triduum officially begins on the evening of Holy Thursday and continues until the evening of Easter Sunday. During this three-day period, the Church celebrates the core of the entire Christian faith, the three historical days that changed the course of history forever.
At the Mass of the Lord's Supper on Holy Thursday, we remember and celebrate the Last Supper, the meal that Jesus shared with His apostles on the night before He was crucified, at which He instituted the sacrament of the Eucharist when He took bread and wine and told His apostles "this is my body" and "this is my blood" and "do this in remembrance of me."
On Good Friday, we are drawn into the most sorrowful of mysteries, the death of God on a Cross. Crucifixion was a painful, shameful way to die, and Jesus willingly submitted Himself to such suffering and ignominy on our behalf, to free us from our sins. We mourn as we recall that, in a very real sense, it was our sins that drove those nails through Jesus' hands and feet.
Holy Saturday is a day of silence and prayer as the Church prepares for the evening Easter Vigil, the "mother of all vigils," when the Church recounts the history of salvation, receives the Elect into the Church, and celebrates the Resurrection of the Lord.
Easter Sunday is the holiest day of the year. It is the day when the Church celebrates Jesus' Resurrection from the dead, by which Jesus gave proof of His divinity and opened for us the way to a new life of grace.
If you've been away from the Church for a while, this would be a great time to give it another try. If you don't even know what I'm talking about, you might try reading the accounts of these events in the Bible: Matthew 26-28, Mark 14-16, Luke 22-24, or John 13-21.