Volume shows how much trading activity took place during each price move. It is indicated with dots at the bottom of the main price chart and in the indicator table on the right hand side (comparing number of up vs down days with high volume over a lookback period preset to 14).
It helps judge whether buyers or sellers are participating with conviction.
Examples include:
stronger volume during a breakout
rising volume as price advances
heavy selling volume during a decline
weak volume during a rebound
unusually high activity near an important level
Volume should not be judged alone. It becomes useful when compared with the price movement.
Volume answers:
Is meaningful participation supporting the move?
Price moving higher with supportive volume is generally more convincing than price moving higher with little participation.