Candlestick charting is a form of ancient charting originated from Japan used to convey – in a graphic form – information of the open, high, low and close of a price movement within a time period. A series of candlesticks or even a single candlestick can provide a history of price movements, which we can use to analyze and predict future price movement.
Candlestick analysis is used by many traders today to improve the success probability of their trades. Highly reliable and accurate, learning how to read candlestick signals efficiently is definitely a skill you should pick up.
Candlestick charting displays similar price information as the bar chart, such as the open, high, low, and close. However, the graphical way in which this similar information is displayed differs. If the closing price is higher than the opening price, then the color of the candle will be light. If the closing price is lower than the opening price, then the color of the candle will be dark.

Candlesticks are formed using the open, high, low and close.
Here is a link to an article which details several candlestick patterns commonly used to read trend reversals.
If you are keen to find out more about using Candlestick to increase the success probability of your trades, I highly recommend Forex Candlesticks Made Easy! by Chris Lee. Written straight to the point in an easy-to-understand style, this is a good guide to learning about Candlestick analysis.