Adding Suppliers: Go to Suppliers and click on Add Supplier >> as shown below:
Here is where you input individual Supplier information. Required fields are indicated in red. You can assign the global commission rate or a specific commission for each Supplier in this view. Any additional Registration Page Fields you created in Settings will appear at the bottom.
(Note: suppliers are currently created individually, not via bulk upload.)
Editing Suppliers: Go to Suppliers and click on the gear icon in the Actions column for that Supplier: