A Candlestick is a type of a price chart that displays the open, high, low and close of specific security for a given time period.
The vertical rectangle of the candlestick represents the real body and can be used to identify if the closing price was higher or lower than the opening price.
Generally, green is used to represent a bullish pattern meaning the closing price of the stock was higher than the opening price and red is used to represent a bearish pattern meaning the closing price was lower than the opening price. Here is a pictorial representation of the same below: