'Triduum Sacrum' means 'the three holy days' -- the culmination of Lent and Holy Week, and the final preparation for Easter Day. Each year the readings for these three days are the same, and in turn the traditional liturgies reflect the events of the Last Supper, the Crucifixion, and Christ's Sabbath rest in the tomb.
The word 'Maundy' is a corruption of the Latin 'mandatum novum', the 'new commandment' that Jesus gives his disciples to 'love one another'. The tradition of foot washing that takes place on this day is a symbolic expression of obedience to that command, and a reflection of what happened in the Upper Room. But the main focus is on the gift of the Eucharist, which is why Maundy Thursday has a celebratory character that the other days of Holy Week lack. There is a reflection and link to the readings at Maundy Thursday
Good Friday is the only day of the year in which the Church does not permit celebrations of the Eucharist lest this should detract from the supreme sacrifice that took place on the Cross. Instead, after the story of the Crucifixion according to John is read, people are invited to express their veneration of the Cross in the physical action of kneeling before it, and to participate once more in the Last Supper by receiving communion from the elements consecrated on Maundy Thursday. There is a reflection and link to the readings at Good Friday
Although nowadays Holy Saturday is often used for children's Easter egg hunts, it ought really to be a day of quiet reflection and prayerful waiting, ending in the Great Vigil of Easter, possibly the most ancient of all Christian festivals. There is a reflection and link to the readings at Holy Saturday