There are two main options for creating new sites on a WordPress Multisite install:

1. Enable users to create their own site using your signup page (e.g. http://example.com/wp-signup.php).
2. Super Admin users create all new sites via Sites > Add New in the Network Admin dashboard.
   

Alternatively sites can be created in batches by installing the following WPMU DEV plugins:

1. Blog and User creator plugin
2. Batch Create plugin

Letting People Register

Enabling registrations so people can sign up for a username and/or site using your signup page is as simple as:

1.  Go to Settings > Settings in the network admin dashboard.

2. Select “Both sites and user accounts can be registered”

• Use “Logged in users may register new sites”– if you want to limit site creation to only logged in users using your signup page
• We recommend that you consider using the following options to reduce splogcreations on your network:
  • Use Limited Email Registrations to restrict who can signup to specific email domains
  • Install Anti-splog plugin

3. Click Save Changes at the bottom of the page.

Adding a link to your Sign-up page on your main site

You need to create a link to your signup page from the front page of your main site so people know where they can register for a site on your network by either:

1. Using a theme that includes an option to add a link to your signup page
2. Adding a link to your signup page
3. Using an admin bar that includes a link to sign up for a site

Your signup page is located at http://example.com/wp-signup.php

Now anyone can sign up as follows using your Sign-up page:

1. Click on Sign-up link

2. This takes you to the sign-up page where you sign up for a username only or username and site.

The signup page on a WordPress Multisite install is located at http://example.com/wp-signup.php whereas on a BuddyPress install it is located at http://example.com/register