The four sections at the top of the dashboard is an overview for the given timeframe.

Please note: the default is Month-To-Date, so the first of the month the numbers will be different than the end of the month.
Income - Based on payment transactions' paid on date within the selected timeframe.
Unpaid - Based on invoices' due date within the selected timeframe. The overall amount of the invoice - the amount paid. Some call it the outstanding amount.
Billed - Based on the invoices' due date within the selected timeframe. The overall amounts of all the invoices.
Users with the Role Type of Billing will see the Billing Overview. To change this setting please go to dropdown under your name->Staff->Edit->Role Type. You must be an Admin or Owner to make this change.