What do understand by GUI?

GUI (Graphical User Interface) includes graphical elements like windows, icons, cursors, and buttons. When you are interacting with a computer, you are the user. The method by which you are interacting is the user interface. All the computing devices now are designed to be graphical. It includes boxes, pictures, lines, and more.

GUIs are designed for different kinds of inputs.

For desktop OS like Windows and Mac OS, the menu bar, small icons, and the cursor is used.

For mobile OS like iOS and Android, larger icons, touch interface like swiping, pinching is used.