The core components of WP-Client are the HUB and the Portal Page. However, the two serve different purposes, and can be used in different ways.
Firstly, by default the HUB acts as the "landing page", that the client first sees when they login. You can have one HUB, or many HUBs, and each client can be assigned to a particular HUB.
The concept is that you can use that HUB to display links to all the content that client has permissions to view, whether it be several Portal Pages or a set of files.
A Portal Page is a page that can be created, and then permissioned to one, several or all of your clients. You can choose who will have permissions when you create a new Portal Page, and you can change those permissions at any time by simply checking/unchecking the appropriate client.
One client can have permissions to many Portal Pages, and many clients can have permissions to each Portal Page