There are two types of relationships you can create on QuickBooks Commerce:
Customer
Customers represent the people/companies who buy from you and appear on your sales orders.
Supplier
Suppliers are the people/companies you buy your products/goods from and appear on your purchase orders.
In the Relationships page, click on either New Customer or New Supplier from the Create New drop-down menu. You can also choose to import your contacts via CSV in bulk. Refer to this article for more information on importing contacts.
This opens the form where you can start entering the company details. Make sure to enter as much information as possible to make it easier to contact and reference the relationship in the future. For customers, you will see a field to select Customer Type to be Business customer or Consumer. Business customers refer to your wholesale customers, usually companies that operate their own retail businesses.
Next, you have default settings to set a few defaults from Tax type to Discounts.
Enter the company's address details. You can add more addresses (Billing, Shipping, Head Office, etc.) from the company's relationship page later. You can leave this blank right now if you want to add addresses later.
Click Create, and you are done. The new relationship should now appear on your relationships page.