These are fixed lines drawn above and below a moving average of price and the width of the band varies with the volatility of the underlying security.
Bands widen when the volatility of the security increases and contract when volatility decreases.
When prices break through a band it usually indicates that the move is strong enough to continue further and sharp moves tend to occur when bands tighten. After hitting a band and not penetrating it the moving average of price will often be the next support or resistance area. OBV is a very popular indicator developed by Joseph Granville and is a running total of volume that reflects accumulation or distribution. Each day's volume is assigned a positive or negative value depending on whether prices closed higher or lower that day and a running total is kept by adding or subtracting the volume depending on the direction for the day. The direction of the OBV line is the thing to watch not the actual level.