Server issue

Hello,
Sir, please provide me the answer as soon as possible.
We have 10 computers in our office connected individually, even server is connected individually, 10 computers are not a part of this server. I want to connect all the computers by Lan connection and connect all computers to the server for assigning policies and permissions and creating user accounts.

What should I need to do and Do I need switch for this?
We are using windows 2012 r2 server