I’ll try one last time, @Lexy_Haughton. You don’t add computers to Manager. If you are running Manager on a server, other computers access the application through their installed web browser. You create user identities that allow them to do that. The procedures for setting up a web-accessible browser have nothing to do with Manager. The procedures for installing the server edition of Manager on a server and creating users are covered in the guides: Guides. Your server’s operating system determines which guide you need.
If you are not qualified to to follow these procedures, you need professional IT support or to subscribe to the cloud edition as @xero50 suggested.