This video provides an overview of the ADX, or average directional index. The ADX is an oscillator used to gauge the strength of a trend. It oscillates between 0 and 100 but hardly ever over 60 unless there are extreme circumstances.
The -DI and + DI indicate direction and crosses are important. More important; however, is the divergence that follows the cross. The ADX is not meant to be used as a stand alone automated trading system.