It has a long upper shadow and typically has no lower shadow. At the end of an uptrend, the long upper shadow is interpreted as a rejection if a key zone like a supply or resistance level is present and the longer the shadow, the stronger the rejection. It has little or no body because the open and close prices are approximately the same or even equal.

It signals a possible change in trend when it appears at the end of an uptrend. It is a strong reversal signal at this position.

Although it is a bearish signal as explained above, it can also appear at the end of a long downtrend and at this position, it signals a bullish momentum from buyers and may lead to a move in price in the upward direction but the strongest signal from this candlestick is mostly when it appears at the top as hinted earlier.

So, how do we trade this Doji?, the easiest method is to short when it shows up at the end of an uptrend and place a stop loss order properly or maybe ensure your risk management strategy is engaged, but more experienced traders don't just jump in, they look for agreement with other signals. They use It in confluence with other confirmations like RSI, section volume and key levels before going short.

Finally, don't forget that it might not work sometimes just like other candlestick patterns. It might give false signals so it gives a stronger signal when it shows up after a prolonged uptrend especially when the bulls are exhausted and lack the momentum to keep driving the market upwards. So make sure to use It in confluence with other confirmations. 

The way I trade it is simple, after some confirmations like those pointed out earlier, I would usually wait for the next candle to form and close below the open or close of this Doji before trading.