A Waterfall chart in Excel is a chart showing how a change in positive and negative amounts affects the total amount. The positive and negative amounts can be based on a period of time (values in and out by quarter, yearly) or based on categories (per revenue source, per segment, per region, etc.) Excel Waterfall charts are also used to display the results of a financial model as it effectively illustrates the incremental impact of each period of time or category.

Just check the site above for more info, and I'm sure you'll know what to do! Good luck!