All computers that are manually operated use a user interface. The user interface is the software by which a user (a person in this case) can operate the computer. User interfaces are broken up into several different categories.
Command-line interfaces
The traditional user interface of which all computers used to be controlled by. A command-line interface allows the user to interact with the computer by typing in commands. The computer displays a prompt, the user keys in the command and presses enter or return.
Graphical user interfaces
Sometimes shortened to GUI. The graphical user interface allows the user to choose an option by pointing a mouse at an icon representing that option.
A common feature of GUIs is that they are easy to use, especially for beginners. They also enable a user to easily exchange information between software using cut and paste or ‘drag and drop’. However they often use up a lot of the computers memory and processing power, making them slower than a command-line interface for expert users.