Step1
Understand What a User Interface Is: The best way to understand what a "user interface" is, is to break the phrase down into two parts: "user" and "interface". "User" refers to the computer's operator; or, the person who is causing the computer to respond.The "interface" refers to what the display device (such as the monitor, LCD, or computer screen) illustrates as the visual output. The interface is the visual stimulus to which the user responds. Whether the interface displays graphics or text, all of what appears visually to the user is the interface.
Step2
Understand What Graphics Are: "Graphics" refer to images, symbols, and icons that appear on the computer screen. Basically, a graphic is anything other than text. Step3
The icons to the left of the interface are graphic representations of specific computer functions and/or operations. Put It All Together: A graphic user interface, or GUI, is a user interface that is created from graphics. For example, Microsoft (MS) Windows operates with a GUI, where symbols are used as icons (these are the graphics), which are accessed by the user to perform specific functions. Typically, icons are symbolically linked to their functions. For example, when a user wants to access their printer through the computer, she will click on the icon that appears as a printer. 
