You spot a bullish engulfing by finding a clear downtrend followed by a small bearish (red) candle, then a larger bullish (green) candle whose body completely engulfs the prior candle's body. Look for an obvious downtrend in progress, a small black candle at the bottom of that downtrend, and a white candle that follows whose body completely covers the black candle.
The second candle should open below the previous candle's close and close above the previous candle's open.
Confirmation comes from above-average volume and the next candle pushing higher, ideally near a known support level.