A customer portal is a way for you to establish a site that your buyers log into where they can search the MLS database, based on the search criteria that you have customized for them.  They are able to interact with the listings and send you messages through the portal.  When your client has used the portal, the portal tab is where you will view information about the listings that have been marked as favorites, possibilities, and rejects.  Watch this brief video tutorial for information on setting up a customer portal for your clients.