Domain Structure for Multisite Network:
you can instal a multisite wordPress network either subdomains or sub-directories.

subdomains: http://site1.example.com
sub-directories: http://example.com/site1/


If you select subdomains, then you will have to configure wildcard subdomains on your server (cpanel) and if you select sub-directories, then you need to do is enable pretty permalinks on your root site.

Enable Multisite
To enable Multisite, you need to access your site using an FTP client or cPanel file manager and open wp-config.php file for editing.

define( 'WP_ALLOW_MULTISITE', true );

Add this line to your wp-config.php file just before the /* That’s all, stop editing! Happy blogging. */ line.
Save and upload your wp-config.php file back to the server.

Setting up The Network

First thing you need to do is deactivate all plugins on your website. Next go to Tools » Network Setup to configure your multisite network.

On the network setup screen, you will get a notice that you need Apache’s mod_rewrite module installed on your server to setup multisite network. This module is installed and enabled on most reputable WordPress hosting providers.

The next thing is to choose the domain structure that you will be using for sites in your network either Subdomains or Sub-directories. After that you would need to provide a title for your Network and make sure that the email address in the Network Admin Email is correct. Finally, click on the install button to continue.

On the next page, you will get some rules that need to add to your wp-config.php and .htaccess file. Use the FTP access,edit those two files and copy paste the code and upload those two files again in the server.

Adding New Sites to Multisite Network

To add a new site to wordPress multisite, simply click on Sites under My Sites » Network Admin menu in the admin toolbar.