What is WordPress Multisite
WordPress Multisite allows users to have multiple sites on a single installation of the WordPress application. The Multisite network owner can manage multiple sites from the same WordPress admin dashboard, including the number of sites, what themes and plugins are active for the different websites, and the separate website’s users and features.
WordPress Multisite is best used when you are creating a network of websites that share similar looks and functionalities. This is because all plugins and themes are shared between the websites and you could configure everything globally for all websites at the same time. If you plan on having differently themed websites or to allow users to manage their own websites’s themes and plugins, then WordPress Multisite is not recommended.
You can read how to install a new WordPress Multisite or convert an existing WordPress into a Multisite in this article.