From your dashboard (or just about any page in Knowify), you will see the vendors section in the top right of the screen:
If you click here you will be able to review your list of vendors, edit any existing vendors, or add new vendors.
To create a new vendor click add new vendor at the top of the page
and fill in the information in the form (most of this is optional as long as you have the vendor name filled in).
Please note that if you use Quickbooks Online, your list of vendors should already be available to you in Knowify as soon as you initially connect the accounts.