In the Charts section you can compare and visualize values. The scale can be picked on the top right.
In the bottom part you select the values to be in the chart. The color of the bars can be changed. Drag the items to change the order. Drag it out of the window to delete them.
Right clicking on a bar gives you option to spilt the values by various criteria.
Clicking on a bar shows a list of the corresponding documents. Double clicking a document will show it. The list can be exported as well.
All the values are shown in your primary currency. The exchange rate can be set in Preferences/Payments
Previous year's values are only displayed in scales that are comparable.
If comparing items, it is most likely that you will get rounding differences compared to the invoices. (This is because taxed are calculated on the total on invoices and not on the individual item)
Charts will become available as soon you have sent documents.