What identifies available computers through the internet?

Using a network connection, including connecting to the Internet, computers connect to each other to transmit data between them and communicate with each other using the TCP/IP (Transmission Control Protocol / Internet Protocol). Think of TCP/IP as a book of rules, a step-by-step guide that each computer uses to know how to talk to another computer. This book of rules dictates what each computer must do to transmit data, when to transmit data, how to transmit that data. It also states how to receive data in the same manner. If the rules are not followed, the computer will not be able to connect to another computer, nor send and receive data between other computers.