To summarise the basics, sockets are the fundamental “things” behind any kind of network communications done by your computer. For example when you type www.google.com in your web browser, it opens a socket and connects to google.com to fetch the page and show it to you. Same with any chat client like gtalk or skype. Any network communication goes through a socket.
In this tutorial we shall be programming tcp sockets in python. You can also program udp sockets in python.