The word "advent" is from the Latin word for "coming," and as such, describes the "coming" of our Lord Jesus Christ into the flesh.
Advent begins the church year because the church year begins where Jesus' earthly life began--in the Old Testament prophecies of his incarnation. After Advent comes Christmas, which is about his birth; then Epiphany, about his miracles and ministry.
The first half of the church year (approximately December through June) highlights the *life* of Christ. The second half (approximately June through November) highlights the *teachings* of Christ. The parables and miracles play a big part here.
Advent specifically focuses on Christ's "coming," but Christ's coming manifests itself among us in three ways--past, present, and future. The readings which highlight Christ's coming in the past focus on the Old Testament prophecies of his incarnation at Bethlehem. The readings which highlight Christ's coming
in the future focus on his "second coming" on the Last Day at the end of time. And the readings which highlight Christ's coming in the present focus on his ministry among us through Word and Sacrament today.
The traditional use of Advent candles (sometimes held in a wreath) originated in eastern Germany even prior to the Reformation. As this tradition came down to us by the beginning of this century, it involved three purple candles and one pink candle. The purple candles matched the purple paraments on the altar (purple for the royalty of the coming King). The pink candle was the third candle to be lit (not the fourth) on Gaudete Sunday, the Third Sunday of Advent. "Gaudete" means "Rejoice!" in Latin, which is
taken from Philippians 4:4.