...
In the Entity field, select the legal entity of your company for which this document is being prepared. The Entity field is available if the Multi-Company Accounting option is selected on the Administration > Settings > General Settings form. The default entity for all users can be selected on the General Settings form. Also, you can specify your personal default entity, for details refer to Personal Settings.
The Basis field is filled automatically, if the invoice is based on a document of the following types: Lead, Quotation, Invoice Received, or Customer Order. If needed, you can manually select the basis document from the list of customer documents (for this, click Show all from the drop-down list). Once the basis document is selected, the data is copied to this invoice. If, after you edited the invoice, you want to cancel the edits, click the Fill in button – the details from the basis document will be copied to the invoice.
...