This tab of the Purchasing Payment Terms Adjustment form provides general information about the change in payment terms used for specific document: Purchase Order, Invoice Received or Additional Expenses. 
The Purchasing Payment Terms Adjustment (create) form. The Main tab
<Auto> in the Number field indicates that an internal number for this document is assigned automatically when you save the document. The From field is populated automatically with the current business date. You can select another date, if necessary.
In the Document field, you can select the document to which the original payment terms were applied. Click the For this, to the right in the field, click the 
(ellipsis) button to open the Select Data Type dialog box.
The Select Data Type dialog box
In the dialog box, select the type of document and then, in the next dialog box, select the particular document of this type. Close the dialog box.
In the Entity field, select an entity of your company which is associated with the document. The Entity field is available if the Multi-Company Accounting option is selected on: Administration > Settings > General Settings. You can select your personal default entity to appear in documents; for this, refer to Personal Settings. If you have not selected your default entity, the entity defined first will be used as the system default value.
You can use the Responsible field to specify the employee who is responsible for the document.
The toolbar buttons
After filling out the tab, click the Save button to save the document. After filling out all the tabs, click Post and Close to save and post the document and close the form.