Connecting to a Server Farm
A SharePoint server farm is one or many SharePoint servers that share the same configuration database, The main important decision you need to make when running the
configuration wizard is whether you want to:
“Connect to an existing server farm”
“Create a new server farm.”
In simple words would you want to attach to an existing configuration database or create a new configuration database?
If you choose to connect to an existing server farm, you are prompted to enter the SQL Server that hosts the database, after which you click Retrieve Database Names,
and then you select the configuration database, please see figure for reference. After that you will need to enter the farm passphrase to join the farm.
By default, this server will also host the web application role, so all web applications, except for Central Administration, will be created and available on this server.
With this information, the wizard can then run. It will configure the files and registry on your server with the proper settings and permissions, and add your server to the SharePoint farm and register it
For the Creation of new server farm . You can consider the blog:
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Hope this help