The easiest way to install WordPress Multisite is to do so via the Softaculous auto-installer in cPanel. More information on how to install WordPress via Softaculous is available in our WordPress Softaculous Installation Tutorial.
To enable Multisite, you need to check the Enable Multisite (WPMU) option on the WordPress installation page in Softaculous. You can then proceed with the installation and once it is completed, Multisite will be enabled in your WordPress