The Advent wreath is a Christian tradition for marking the four weeks before Christmas by lighting a new candle each Sunday. Sunday is the preferred day since it is the Sun's day. Pagans adopting the same custom might light a new candle each Sunday for the four Sundays before Winter Solstice.
Gertrud Mueller Nelson in To Dance with God talks about how people in the far north removed wheels from their carts during the depth of winter. They brought these wheels into their homes and decorated them with evergreens and candles. This, Nelson says, is the possible origin of the Advent wreath.
An Advent wreath is a circle of evergreens with places for four candles. When I was growing up, we always used three violet candles for penance and one rose-colored candle (lit on the third week, which is called Gaudete (Rejoice) Sunday) to symbolize the coming joy. Nelson says in her family, they use the traditional red candles and red ribbon to decorate their wreath. I like to use candles in the colors of the four directions: yellow for east, red for south, blue for west and green for north.
Helen Farias in The Advent Sunwheel, her book of suggestions for pagans wanting to celebrate Advent, points out that the Advent wreath, made of greens in a circle shape and lit by candles is a potent symbol. The circle with the dot inside has long been a symbol for the sun and is still used that way in astrology. Helen suggests putting a fifth candle in the center of the Advent wreath, to be lit on the solstice, to make the symbolism more apparent.
There is another kind of wreath which is found in Germany and Scandinavia, made of apples and dowels (chopsticks would work too). Three apples with dowels connecting them in a triangle form the base and the fourth apple is suspended by dowels above the rest, forming a pyramid. The triangle and pyramid are also both sun symbols.
Farias, Helen, The Advent Sunwheel, Juno's Peacock Press (out of print).
Nelson, Gertrud Mueller, To Dance with God: Family Ritual and Community Celebration, Paulist Press 1986