Dark Cloud Cover is a combination where the body of the red candle starts below the body of the green candle. The red candle follows the green one, while the closing price of the red candle is in the area of the lower part of the green candle body.
As a rule, this pattern gives a signal about the beginning of a downtrend. Dark Cloud Cover works similarly to Bearish Engulfing, but it is not as strong. To confirm the signal, analyze other patterns as well.