Multisite is a feature of WordPress that allows you to use one installation of WordPress to power more than one WordPress website.
See How to turn on WordPress Multisite? for instructions on how to activate Multisite.
Once Multisite is activated, you’ll have a new “My Sites” menu at top left of your WordPress dashboard.
Under My Sites, you’ll have Network Admin.
In Network Admin, you can go to the Plugins page, where you can “network activate” plugins. This means the plugin will be activated on all of your Multisite websites.
In Network Admin, you can also go to the Themes page, where you can “network activate” themes. This means the theme will be available for activation on all of your Multisite websites.
Under My Sites > Network Admin > Sites, you can edit your Multisite website URLs. If you’d like to use a custom domain name for one of your Multisite websites, that domain name will need to be added as an add-on domain or alias in cPanel. To do this, login into your website control panel, search for Addon Domains, (or Aliases), and add your domain.How to turn on WordPress Multisite?