In Global Financial Accounting Settings you could define Document Types. Those are used to control and segregate your entry transactions based on the business processes you defined. The SAP ERP is coming with plenty of standard document types which will would be nice if you can use out of the box. It will ease your maintenance.
IMG Path: Financial Accounting (New) -> Financial Accounting Global Settings (New) -> Document -> Define Document Types for Entry View
Table: T003, T003T
When you enter into the transaction, click on “New Entries” to create new document type or double click on existing one.
On the screenshot below you will see how the standard document type for vendor invoice is defined. Maintain based on your requirements.