The Waterfall visualization (often called a progressive bar chart) combines a column chart with a line chart. In effect, it lays out the incremental data as individual columns that add incrementally to the total. Visually, each record provides you with a proportionately sized column that is added to the total over time. It is a great visual for showing unit and sales growth.
These three graphs display the same data to compare the Waterfall Chart with the Column Chart and the Line Chart.
You can visit the Power BI tutorial at support.powerbi.com.