Once you've added your web part to a page, click the Edit button to display the properties:
The properties pane will now appear on the right.
In the properties pane, select a chart type add the URL to the SharePoint List containing the raw data you want to visualize:
As you enter the list URL you'll be presented with drop-downs containing your list fields.
This is the field which will be used for the Y axis, or will be used to represent the size of 'slices' in the case of a pie chart. It's the primary data you want to visualize. In this case, we've picked Revenue, and it'll be reflected in the size of the bars:
This is the field which will be used for the X axis, or the labels for the separate 'slices' in the case of a pie chart. It's the field which will be used to group together and aggregate the numerical data.
By default, the SUM aggregation is applied. This will add together every value for each grouping:
Aggregations available are:
None: no aggregation. Every individual list item is rendered as a data point.
Sum: adds each numerical item, grouped by the 'grouping' column
Item Count: number of items for each group
Average: average value within each group
Maximum: max value within each group
Minimum: min value within each group
Standard deviation: the standard deviation within the group
Variance: the variance within each group
You may wish to visualise sub-categories for each category in the data. For example, the chart above displays Revenue by region. However, you may want to further break the values down by another field - in this case sales stage: