Bearish Engulfing pattern is just mirror image of bullish engulfing pattern with bearish implication.
First, we should be having an up-trend. Then we should have a green candle as continuation.
The next day should see a gap up above the close of previous day. The 2nd day candle should eventually close red with its body totally engulfing the body of the first candle.
The confirmation comes when within next 2-3 candles the price moves below the low of the two candles forming the Bearish Engulfing pattern.
On confirmation a trader may take a short trade with stop loss above the top of the two candlestick patterns. Larger the 2nd candle, more bearish is the pattern.