To send a sales/expense invoice to accounting , click Send to accounting from the preview of your documents:
Immediately, the button changes and displays Accounting lines: your accounting lines are now awaiting export and ready for accounting.
You can check the entries by clicking on the button:
At this point, the entries are awaiting export.
As long as you have not exported your data, you can cancel the accounting records (eg in case of last minute changes) by clicking Cancel accounting.
Once your export is done, entries will be locked. You can always unlock them if necessary from the same window.