You don't have to assign vendor numbers to everyone.  You may have vendors from which you only order once or very infrequently.  In that case, just enter their name and addresses on the Main Purchase Order Screen.  No number is needed.

If one of your infrequent vendors later buys from you again, you won't have to re-type their address.  Just click the "L" button beside the "VENDOR" field on the Main Purchase Order Screen.  A list of all past vendors will appear from which you can select:

You can also access this list by placing your cursor in the "VENDOR" field and doing the following:

Note that pop-up list described here consists of all vendors on previously issued purchase orders.  That's different from the Vendor Database.  The Vendor Database consists of vendors to which you have specifically added to the database and to which you have assigned a number.  (The Vendor Database can be accessed by clicking the "L" beside: "Vendor #"  More information on that list is found here.)

You'll want to use one of the above methods for entering Vendor Names, particularly those without numbers.  That way the name and address will be spelled the same, and you'll be able to use the search and filter processes effectively.