Beginning the Church's liturgical year, Advent (from, "ad-venire" in Latin or "to come to") is the season encompassing the four Sundays (and weekdays) leading up to the celebration of Christmas.
The Advent season is a time of preparation that directs our hearts and minds to Christ’s second coming at the end of time and to the anniversary of Our Lord’s birth on Christmas. From the earliest days of the Church, people have been fascinated by Jesus’ promise to come back. But the scripture readings during Advent tell us not to waste our time with predictions. Advent is not about speculation. Our Advent readings call us to be alert and ready, not weighted down and distracted by the cares of this world (Lk 21:34-36). Like Lent, the liturgical color for Advent is purple since both are seasons that prepare us for great feast days. Advent also includes an element of penance in the sense of preparing, quieting, and disciplining our hearts for the full joy of Christmas.
As we prepare for Christmas, the General Instruction of the Roman Missal notes some differences to the Mass that should be observed during the season. For instance, the priest wears violet or purple during Advent, except for the Third Sunday of Advent (Gaudete Sunday) when rose may be worn (GIRM, no. 346). Aside from what the priest wears, other aesthetic changes in the Church can include a more modestly decorated altar.
The final days of Advent, from December 17 to December 24, we focus on our preparation for the celebrations of the Nativity of our Lord at Christmas. In particular, the "O" Antiphons are sung during this period and have been by the Church since at least the eighth century. They are a magnificent theology that uses ancient biblical imagery drawn from the messianic hopes of the Old Testament to proclaim the coming of Christ as the fulfillment not only of Old Testament hopes, but of present ones as well.
Advent devotions including the Advent wreath, remind us of the meaning of the season. Our Advent calendar (linked below) can help you fully enter into the season with daily activity and prayer suggestions to prepare you spiritually for the birth of Jesus Christ.  
 

“What’s a Vespers?” Ah… You must have seen that we’re having Advent Holy Hours with Vespers starting up in just a couple of weeks! Vespers—also simply called Evening Prayer—is part of the Liturgy of the Hours or Divine Office (those two titles are interchangeable). The Divine Office is a liturgical arrangement of Psalms, Hymns, Canticles, Scripture Readings, writings from the Saints and other spiritual authors, and Intercessions that
are prayed at seven different times throughout the day. “Office” comes from a Latin word that means a “work” or “duty” (Latin: officium). Saint Benedict, who arranged the Psalms and Readings of the Divine Office as part of his monastic Rule, expected his monks to dutifully participate in this “work of God” every day as part of the contemplative life. 
In many Benedictine monasteries of monks and nuns, they still pray the Divine Office in the manner laid down by St. Benedict—complete with beautiful chant, incense, and great solemnity. The simplified version of the Divine Office prayed by most Priests and Consecrated Religious is called The Liturgy of the Hours. So, if you ever hear a Priest talking about “praying
his Office,” this is what he’s referring to! Despite their name, the prayers throughout the day don’t take anywhere near an hour to pray. In fact, most “hours” take between five and ten minutes to pray when recited. The “hour” refers to the fact that the Liturgy of the Hours is generally prayed at or near certain hours of the day. The prayer prayed at the “evening hour” is
called Ad Vesperem in Latin, which basically means “at the evening hour”. In English, we just call it Vespers or Evening Prayer.
While Priests and Religious are mainly the ones who pray the Liturgy of the Hours—in fact, we’re obliged to—anyone can participate in the Church’s daily liturgical prayer by praying it. This is a great way to “live liturgically” because the prayers of the Divine Office change based on the day, the Feast, the Saint of the day, the Liturgical Season, and even the time of day. So, it really helps to anchor a person in the Church’s liturgy every day, even if they can’t attend daily Mass. At our Advent Holy Hours, before concluding with Benediction, we’ll pray Sunday Vespers together. Don’t worry—it’s really easy, I’ll have handouts printed, and I’ll give you clear instructions beforehand. If you find that this is something you enjoy doing, and perhaps even want to incorporate into your own life, you might consider downloading the iBreviary app,
which allows you to pray the Liturgy of the Hours on your phone or tablet without having to worry about flipping pages or setting ribbons. See you at Advent Holy Hours, and please invite a friend (or ten)!

The use of the Christmas tree is relatively modern. Its origins are found in the medieval mystery plays that depicted the tree of paradise and the Christmas light or candle that symbolized Christ, the Light of the world. According to custom, the Christmas tree is set up just before Christmas and may remain in place until the Solemnity of Epiphany. The lights of the tree are illuminated after the prayer of blessing.
 
 In the home the Christmas tree may be blessed by a parent or another family member, in connection with the evening meal on the Vigil of Christmas or at another suitable time on Christmas Day.