Name and registrations
Taken from: The WordPress MU Manual
This is where you can change your Site Name.
Site Admin Email
Insert the email address for your site admin.
Allow new registrations
Determines who can create new usernames or blogs.
Your options are:
1. Disabled – all usernames and blogs must be created by site admin user
2. Enabled. Blogs and user accounts can be created – anyone can create blogs using your signup page (e.g. http://writerspot.blogs.mu/wp-signup.php).
Tip: If you use this option you might want to Limited Email Registrations to specific domains to restrict who can signup.
3. Only user account can be created – anyone can create a username but all blogs must be created by the site admin use
4. Only logged in users can create new blogs – Users can create new blogs using your signup page but all usernames must be created by site admin user
Registration notification determines if site admin receives an email notification every time someone registers a blog or user account. On a large blogging site you would select No.
Next up… user options.