This section is applicable to the MSP Edition [Central only].
Partners are one level up to Customers, who can otherwise be called as Direct Customers. Separate list views are available for the Customers and the Partners in the Customer / Partner wizard of Admin Tab.
On the other hand, Partner Customers are those added under the existing Partners. Sites and Probes are the two entities associated with both the Direct and the Partner Customers.
Now, click each of the below links to learn on how to manage the customers, along with sites & probes, the partners, and the partner customers:
Managing Direct Customers and Sites
Associating Probes to Sites
Deleting Customers and Sites
Editing and Deleting Partners
Partner Customer Management