The accounting report summarizes all the completed expenses until the end date you choose.
To create the accounting report, click on the 'Reporting-button' next to the 'Adding expenses'-button. Via the dropdown you can select 'Create accounting report':
Select an end date and click 'Run accounting report'.
You will see a draft version of the report on your screen where you can review the expenses. Choose to what extension you want to export your report by clicking on the 'Export report-button'.
Wait for the wheel to stop spinning. Download the report by clicking the 'V'-button.
To be sure not to forget to mark all expenses as reported - so that they will not appear in the next accounting report and you can be sure all expenses are only paid back once - you can set this option as a default in your 'Personal settings' by checking the box before 'Activate set as reported for accounting reports by default'.