You would need to establish a LAN if there is none so far. The hardware apart from PCs/laptops needed for this is switch and network cables mentioned in a previous answer That is only the infrastructure needed for any file sharing chat and other services. I assume you have Ubuntu as desktop laptop systems. Such systems needs to be connected over the LAN.
Samba is for sharing files to windows if you use.
- Native Linux utilities like telnet, ftp or more secure ones sftp, ssh will provide for data transfer between systems.
- Intranet webserver will help you if you need share common data to be accessible to others.
- Jabber can be used to setup chat.
- If you opt for internet service and need to share, squid as a proxy can help you.
Giving step by step instructions to be these is not possible here.
So how you can go about it.
About LAN setup and TCP/IP setup - read any network basics book / article on internet.
TCP/IP on Ubuntu, you can get it from help.ubuntu.com
Ubuntu server manual describes, how to install and setup a server for hosting many of these services.
If you like specific help on anything post another question on those areas after mentioning your OS version as well.