No, someone who registers will be classified as a prospect initially and you get notified via email of their registration. Then you decide if you want to have them login. That is in order to prevent people from accessing your private portal and resources without you assessing their identify and registration first.
To activate them, click on the CONTACTS TAB, scroll to the "Prospect" section of your contact list and click on their name. Click on the "Profile" tab. At the top of the Profile page, you will see the statuses of Active, Hot Lead, Inactive, Prospect, and Buyer. Simply click on the radio button next to "Active" (or "Hot Lead", whichever you prefer), and save the change. This will activate their account and will now "turn on" the username/password the client created when they registered on your site.