An Advent Wreath is usually made from a circle of evergreens and candles. Four candles mark the four Sundays of Advent and sometimes a fifth one is placed in the centre to be lit on Christmas Day. Usally three of the candles will be purple (the colour of Advent) with a pink one for the third Sunday. The central candle for Christmas Day is always white.
The weblinks will give you some ideas for creating a wreath to use at church, school or in the home. You will also find suggestions for prayers and readings to use as each candle is lit.
The book Together for a Season: Advent, Christmas and Epiphany has suggestions for using the wreath through Advent and beyond in worship, children's groups and school.