The church year is divided into seasons, rather like the solar year, except there are more of them. It consists of two cycles of feasts and holy days: one is dependent upon the movable date of the Sunday of the Resurrection (Easter Day); the other, upon the fixed date of December 25, the Feast of our Lord's Nativity (Christmas Day). Easter Day is always the first Sunday after the full moon that falls on or after March 21. It cannot occur before March 22 or after April 25.
Advent begins a month before Christmas, and in the midst of the gift-buying/ making/giving flurry is a time of contemplation and preparation. Typically, carols aren't sung during Mass, there being an entire section of the hymnal devoted to Advent.
Christmas begins on Christmas Day, and lasts 12 days. Holly, poinsettias, pine boughs, and white candles grace the sanctuary, and finally we get to sing carols.
Epiphany celebrates the coming of the Wise Men and the return of light to the world, even though here in the North we still have to wait another month for the daylight hours to increase. Epiphany lasts until Shrovetide, the Sunday, Monday, and Tuesday immediately preceding Ash Wednesday.
Ash Wednesday marks the beginning of Lent. The palm leaves and palm crosses so joyously displayed during Easter have been drying, and now they are burned. The ashes are used to remind us of our mortality -- that we are made of dust and to the dust we shall return.
Lent commemorates the 40 days Jesus spent in the wilderness, and is a time of contemplation, penitence, and preparation. It is traditionally observed by giving up things -- chocolate, video games, purple nail polish, or competitive overhand refrigerator tossing on Friday nights when it's hard to get a sitter anyway. Lent isn't about giving up external things, but internal things -- fear, envy, pride, dishonesty. Lent ends on Palm Sunday, the Sunday before Easter.
Holy Week runs from Palm Sunday to Holy Saturday, and includes Maundy Thursday and Good Friday. It replays the events from Jesus' ride into Jerusalem through the Crucifixion. "Jesus Christ Superstar" was about Holy Week, not Easter.
Easter dawns chilly, bright, and, in some years, snowy. The weather doesn't matter -- the Lord is risen indeed, and the church is full of lilies and palm leaves and little girls in big bonnets. Hallelujahs! ring from the rafters. Easter lasts until Pentecost.
The Day of Pentecost, also known as Whitsunday, celebrates the coming of the Holy Spirit to the apostles and to all of us.