the bars on the left trace volume by price, the y axis, of the chart.
so it is a volume record by price level.
more traditional charts show volume by time period, the x axis, at the bottom of the chart.
These types of charts are useful to find places where people have bought a stock in the past, to help look for levels where people may buy again in the future. It helps see levels of support and resistance.
Market Data 
Markets 
AI
