The Rcpt. by Vendor Function works in basically the same way as the Receipt Function with the difference being that you do not have to enter in the Document No you want to process.  When using this Function you should enter in the Vendor No you have received the items from instead.

Once the Vendor No has been entered, you will then be presented with a list of all the Purchase Orders for that Vendor which currently have Items outstanding.  You can click on the Arrow button at the top right in order to view some more information if relating to the Purchase Order if required.

You can then select the required Purchase Order from the list and then proceed through in the same way described against the Receipt Function to in order to process the receipt.