The reason that the Internet works at all is that every computer connected to it users the same set of rules for communication. Do you know that set of rules is called Protocol ?
A Set of rules is called Protocol.
The communication Protocol used by Internet is TCP/IP. The TCP (Transmission Control Protocol) part is responsible for dividing the file into packets on the source computer. It (TCP) is also responsible for reassembling the received packets at the destination computer.
The IP (Internet Protocol) part is responsible for handling the address of destination computer so that each packet is sent to its proper destination.