MACD is one of most popular technical anlyis tool in forex trading. The following is a MACD video series consisting of two videos. In these videos the author explains how to use the MACD indicator.

The author also explains the following.
The most common formula for MACD is 12,26, 9 formula.
MACD is made up of the difference between the value of 12 day and 26 day exponential moving averages.
Then a 9 day exponentail moving average of the MACD is superimposed as the siganl line.