The word "harami" means "pregnant" in Japanese. This is explained by the shape of the two-session indicator, with the second day entirely within the trading range of the first.

However, this pattern is only reliable as a reversal signal about half the time. So by itself, it cannot be relied upon to take action in either entering a position or exiting it. You need more.

The harami serves as confirmation, however, for other reversal signals. So if you see a signal in the firm of a candlestick pattern, move beyond resistance or support, gapping prices, volume spikes, or changes in momentum, you need to find confirmation. If a harami appears that tells you the likely reversal will move in the direction you expected, it is one of many worthwhile confirming signals.

The bullish version of the harami starts out with a black (downward-moving) session. The next session opens and closes within the range of the first and is white (upward-moving). 

In the bearish version, you find the same relative pattern between the two sessions; but the first session is white and the second is black.

Any candlestick indicator can serve as confirmation; but this particular one is only good for that, and cannot be used as a signal for reversal. Any 50/50 chance is of no value at all by itself. You need more. However, as a lagging indicator confirming a different signal, the harami adds to your confidence that a reversal is likely to occur in coming sessions.

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