When you are installing multisite, There are two possibilities for the condition of the website.
A fresh website = Installing a multisite network on a fresh WordPress installation.
Existing Website = Have an existing site on which multisite network is required to be installed.
How to activate WordPress multisite on a fresh website
Installing With Hosting Installers:
To install multisite in your fresh website you have to go to WordPress installer in your hosting provider’s dashboard.
From the dashboard, you just have to select the install WordPress multisite option on the bottom and it will be installed within some minutes.
Installing WordPress Multisite Network In Kinsta
This is the multisite installing setup for fresh websites. Here you have to select which type of multisite network.
It gives options for subdirectory and subdomain option.
subdomain format is – subdomain.domain.com
and sub-directory format is – domain.com/subdirectory
there are so many factors that you have to keep in mind before choosing this option because it is not easily revertable process.
Must read this before deciding the format of the domains. Click here to read
Installing WordPress Multisite Network In Siteground
The above shown is the setup to activate WordPress multisite. You have to select the domain, language, username, Admin email, and give a strong password with allowing multisite network.
In siteground choosing, the domain is not decided at the time of installing the core WordPress.
To select the structure of the domain go to settings or tools > Network Setup > Choose the type of address you want > and install.
After that, you have to login again into your WordPress dashboard.
After accessing your WordPress dashboard, the My sites option will be added to your backend.
Choose network admin > Dashboard.
To access the admin site settings.
You will see the Settings tab in the super admin dashboard.
Go to Settings > Network Setup.
Here you all the settings regarding the network is given.
to install Multisite Network manually, you need to access the File Manager of your Hosting Service Provider’s Dashboard.
After accessing the file manager folder of your website, Find wp-config.php file
file manager in cpanel
To start, open up the wp-config.php file. In that file, find this line: (you will find it at the very end)
/* That's all, stop editing! Happy blogging. */
Immediately above it, add this line of code:
define( 'WP_ALLOW_MULTISITE', true );
Now save your file.
Go to the site’s admin. Then go to the Network Setup screen (via Tools > Network Setup).
In-Network setup choose the format of the domain from subdomains or subdirectories. (Click here if to know more if you don’t know which to choose)
Enter the title and admin email address for your network in the relevant fields and click the Install button.
Here you will find some code, copy and paste it into stated files: the wp-config.php file and the .htaccess file.
Super Admin tools tab for network setup
Note: Copy-Paste the code only given in your Backend’s tools tab.
The set-up is complete. Login again to access your Multisite network.
About the second option:
How to activate WordPress multisite on a existing website
On websites that are older than 1 month then you will find any option for choosing the structure of the domain. It does not allow to create subdirectories if the site is more than a month old.
Why? It may cause fatal errors for some premade URLs.
suppose you have created a website for “domain.com/knowlegebase” and now you are making a subdirectory named knowledgebase then URLs may clash because the subdirectory will create URL as domain.com/knowledgebase.
If WordPress allows users to choose the structure type, then only it is possible to make subdirectories otherwise it is fixed to have a subdomain structure.
The process of installing is same as manual process showed before.