L&S CVD is made of different things: green bars, red bars and a black line.
This indicator looks at which volume brings the price higher or lower. When the volume exchanged increases the price it is taken into account positively (Bull volume). Whereas the volume that drives the price lower is taken into account negatively (Bear volume). The sum of the Bull and Bear volumes is the Cumulative Volume Delta (CVD). The CVD is displayed as a histogram: when there is more Bear volume than Bull volume the CVD is negative and it is displayed with red bars. When there is more Bull volume than Bear volume the CVD is positive and is displayed with green bars. To sum up, it tells you in which direction most of the volume is exchanged.
The Black line is simply a moving average of the CVD, and indicates the trend.