Candles used to be the main source of light for people long ago before light bulbs and electricity were invented. Candles are made out of a piece of string, or wick, which is surrounded by wax.
When the candle is first lit you set the wick on fire but once the wick is burning it melts the wax, so after that first few moments the candle burns the wax not the wick.
The ceiling is the part of a room that is directly above the floor. Ceilings are usually painted white and sometimes have lights like chandeliers on them.