As shown on the chart, when the MacD falls below the signal line, it is a bearish signal which indicates that it may be time to sell. Conversely, when the MacD rises above the signal line, the indicator gives a bullish signal, which suggests that the price of the asset is likely to experience upward momentum. You may wait for a confirmed cross above the signal line before entering a position in order to reduce the chances of being "faked out" and entering a position too early.
The color of the Histogram may help you too to determinate the top to sell or the bottom to buy.