It is a 2 candlestick bearish pattern and just opposite of Bullish engulfing candlestick pattern. It warns about a potential Bearish trend that may approach soon.First candlestick of the pattern is a Bullish candle while the second one to be large Bearish candle with a length enough to engulf the first candle completely without the regards to length of tail or shadows of the candle. This apprehends that the second candle of the pattern have it's opening price above of the close price of first candle while the closing price of the red candle to be below of closing point of first candle.
The first candlestick of the pattern can be a Doji candlestick while the second one can be a Marubozu candlestick .

Being a pattern just opposite of Bullish Engulfing candlestick pattern , it recommends you to sell the current position while bullish engulfing patern suggests you to buy the stocks.After a bearish engulfing pattern appears, you may also do trade by short-selling technique.

Studying the Bullish engulfing pattern

It is preferable if the Bearish candlestick of the pattern has a long real body with a small lower shadow.As the body length is long, it signifies that the price had been significantly depleted below the opening price and the short wick suggests that there is not much difference between opening and lowest price of session which makes it more likely to have the next candle to be a Bearish candle.
One more thing to take note is that more are the preceding bullish candlesticks before the pattern, more is the chance of trend reversal. Bearish engulfing pattern becomes more significant and likely to show trend reversals if preceded by 4 or more green/white candlesticks.

Trading or working with Bearish engulfing pattern

You are always adviced to never make a trade solely based on candlestick pattern. Though, if you decide to trade by observig any pattern you should look for any other signal or indicator as a confirmation.
If the candle next to the Bearish engulfing pattern opens Gapped-down , it is a very good sign for the pattern . As a Bearish candlestick pattern, you should consider it as a reversal pattern only if it appears during a clear downward trend ,otherwise it can just be a continuation pattern. It is not of much significance during a choppy market .
Stop-loss - Talking about the stop loss than it can be placed at the topmost point of the first candle of pattern.Though ,it is totally up to you about what amount of risk you can take and thus put the stop-loss.

General advice on trading with Bearish engulfing pattern :

       Never consider the indication provided by the candlestick to be 100% trustable, as they represent only low, high, close and open price of the session to which a particular candle represent.Moreover, we consider long Bearish candlestick in the pattern to be good, but it also increases the range of stop-loss and the returns may not be worth it. But on the same time these patterns can be very much useful and profitable if traded wisely and carefully.You have to also check other indicators to make an exit from the trade as these pattern don,t provide you any target price. If you think to exit the trade based on any signal given by candlestick at a particular instant , than you may be partially correct but tools like support and resistance are very useful for exiting the trade.