A Candle or Candlestick is a charting tool that is used to express of price action of an asset within a certain time frame. A candle can be drawn for any time frame, but typically it is denominated in minutes, hours, days, weeks and months.
Candlesticks specifically show 5 metrics;
1) what was the price of an asset at the start of the candle (open)
2) what was the price of the asset at the end of the candle (close)
3) what was the highest price of an asset during the candles time frame (High)
4) what was the lowest price of an asset during the candles time frame (Low)
5) what time frame is the candle covering (time)
Candlesticks are commonly encountered in two colors, red and green. (although many professional traders & investors customize candles to be any color of their liking) Red candles show that the price of asset went lower in relation to the candle immediately before it. Green candles show that the price went up relative to the candle immediately before it.