Interface

An interface or shell is what the user uses on an operating system to make the computer do tasks, like writing a document, or loading a web page. There are two types of interfaces, a command line interface (CLI for short) - where people write commands to make the computer perform tasks, or a graphical user interface (GUI for short), where people use their Computer mouse to click on buttons to perform tasks.
Command line interface.
"See Command line interface."
Command line interfaces ask the user to type in commands in a text-based environment, not allowing images, like the screen image to the right.
For example, if the user wanted the computer to say "Hello World", he or she would:
This is hard to use for most people, mostly because when the user has to do a long command, he or she can miss a letter or two, so the computer shows an error, and he or she has to do it all over again, which can waste hours.
Graphical user interface.
"See Graphical user interface."
Graphical user interfaces are instead made of not only text, but also images. The first computer to do this was the Apple Lisa (1983).
The following operating systems can use graphical user interfaces:
Since the top operating systems (listed above) use graphical user interfaces, they are seen on every computer. Anyone can still use a command line interface on any computer very easily.