The purpose of TCP/IP is to make it easier for computers to communicate with one another to send information over the Internet. It is a set of protocols that computers use so that they essentially speak the same language when passing information.
TCP/IP tells the computer how to put together data packets before they are sent across the internet, and it breaks these packets down into small bits. It does the opposite on the other end, reassembling them so that they make sense to the receiving computer. The TCP/IP protocols determine how the information is sent, tell the computer how to address them and move them across the Internet.