Hello:
Go to the Company Profile and select the Integration tab. You will see a list box labelled "G/L Description 1". Choose "Vendor name" from the list of choices.
Note that this setting will be used for Invoices, Adjustments and System Cheque runs.
If you want to include more than just Name in the Description (ie. Document # and Vendor name), then choose "User-Defined" from the list. Then you must edit the fields labelled "Batches user defined format" and "Other user defined format". In each of those fields, you would specify the fields that you want in the Description. The codes are a little obscure - click on the "Help" button to see the choices. For instance, %dno %vnm would send Document # and Vendor name to the GL.
The second field, "Other user defined format", is used for System Cheques and Cheque Reconcilation postings.