Hello,
Its a symbol to represent that Jesus is the Light of the World.
We always had a Christingle service at school when I was at primary school and that was 30 odd years ago.
A google search told me that it started in 1747 but became popular in the UK in 1968.
A Christingle usually consists of:
-An orange, representing the world
-A candle pushed into the centre of the orange, then lit, representing Jesus Christ as Light of the World
-A red ribbon wrapped around the orange or a paper frill around the candle, representing the blood of Christ
- Dried fruits and/or sweets skewered on cocktail sticks pushed into the orange, representing the fruits of the earth and the four seasons. Cloves can be added as well.