Depends on your level of expertise. The entire purpose for developing windows was so that there would be a User Interface for computers. Ever tried working on code without a user Interface? If you are using internet Explorer, Press the buttons Alt, then V, then C. That is what you would be looking at if there were no interface. If you are Using Firefox, press Alt, then V, then O.
Kind of hard to read all of that Huh?
The short answer is that it makes a computer and/or software way more user friendly.
The user interface is software.
Graphical User Interface
This is what the user sees and works with when using the computer..Different types are Graphical user interface, Command line interface and Manual driven interface
when the window is user friendly then we can easily use the user interface.
Graphic User Interface (user-friendly)
Graphical User Interface
Magic User Interface was created in 1993.
When an interface is easy to use it is normally referred to as a user friendly interface. A friendly user interface saves time and does not require any special skills to operate.
Graphical User Interface.
Aqua - user interface - was created in 2000-01.
Graphical user interface
The 'shell' is a user interface program that interfaces between a user of the system and the Operating System. It is the user interface.