An intranet is a private network accessible only to company staff. So, only company employees can share information using this kind of network, and other people can not read it or use, unlike the Internet.
An intranet uses TCP/IP, HTTP, and other protocols like the regular Internet. Using tunneling employees can send private messages through the public network by means of encryption/decryption. Usually, companies allow their employees to use their intranet to access the public Internet through firewall servers.