What does GUI interfaces mean?

Graphic User Interface. One of the main uses is so that you can use a mouse to interact with your computer. The system lays out your screen as a grid and "knows" where the cursor is and where your icons are with respect to that grid. When you "click" your mouse button, the computer checks the cursor's location and compares it to the graphic objects(such as icons) and does whatever action it is programed to do. For example if you hover the cursor over the icon for internet Explorer and double-click(in Windows), the computer starts your IE browser.