...

In the Supplier field, specify a company or other legal entity from whom the payment is received. Select it from the Companies list. 

<Auto> in the Number field indicates that a number to this document will be assigned automatically when you save the document.

...

In the Comment field you can specify some additional information.

The toolbar buttons

After entering some data on the tab, click the Save button to save your work. After filling out all the tabs, click Post to post the document without closing it or Post and close to post and close the document. 

...

For other button descriptions, see Document Toolbar.