What is the Internet? essentially it is a world wide collection of inter connected network of computers. Hence the word Internet.
An important aspect of the Internet is that it all connected through a series of standard protocols. These protocols (agreed rules, a.k.a TCP) allow computers to communicate with each other consistently through the network.
Each computer, especially major backbones, are assigned IP (internet protocol) addresses or less major computers via NAT (Network address translation) network to identify where data (often in packets) is sent, right down to the individual device. IP addresses, or more specifically IP v4 are in the form 192.7.78.45
A map showing how the world's internet computer systems are connected to each other.
source: telegeography.com
Most of the internet is experienced through web browsers or web applications viewing websites with a range of computing devices from portable devices such as smart phones , tablets to desktop computers.
A simplified diagram showing the parts of the Internet and how it is connected to each other. image: clearlyexplained.com
Culture of the internet
This deals with the history of the internet and how it relates to society in general. It considers things such as how the internet extends human behaviours and creativity.
For example the use of rapid dispersion of ideas such as memes, news articles or other forms of information and how this influences daily thinking or psychological processes of peoples or groups of people (communities).
It may also consider the way in which different cultures, societies sub cultures treat the internet.