Why do we celebrate Advent?

The Catechism of the Catholic Church (paragraph 524) says,

"When the Church celebrates the liturgy of Advent each year, she makes present this ancient expectancy of the Messiah, for by sharing in the long preparation for the Savior’s first coming, the faithful renew their ardent desire for his second coming. By celebrating the precursor’s birth and martyrdom, the Church unites herself to his desire: “He must increase, but I must decrease."

How do you prepare yourself during Advent?
How do you observe Advent?
What do the 4 candles of the Advent Wreath represent?

O Glorious St Michael, Guardian and Defender of the Church of Jesus Christ, come to the assistance of the Church, against which the powers of Hell are unchained.  Guard with thy special care her august visible head, and obtain for him and for us that the hour of triumph may speedily arrive.  O glorious Archangel St Michael, watch over us during life, defend us against the assaults of the demon, assist us especially at the hour of death, obtain for us a favourable judgment and the happiness of beholding God face to face for endless ages. 

Amen.