How to Allow User Registration on Your WordPress Network
When you enable your WordPress network, new site and new user registrations are turned off, by default. However, as the network administrator you can add new sites and users from the WordPress Network Admin Dashboard. To let users sign up for your network, complete the following steps:
1Click the Network Admin link at the top of the Dashboard and then click the Settings menu link.
The Settings page loads in your browser window.
2In the Registration Settings section, select the User Accounts May Be Registered option.
This allows users to register on your network, assigns them to the main site as a Subscriber, but doesn’t allow them to create a new site of their own.
3Click the Save Changes button at the bottom of the page.
Both sites and user accounts can be registered on the Network Admin Settings page; you have allowed users to register a new account and given them the option to create a new site on your network.