A GUI or Graphical User Interface is basically just what you see on a computer screen, and it grants users the ability to be able to interact with components on the screen using the mouse, like clicking on a website link or scrolling down a page. Some examples of Graphical User Interfaces are;
Here’s a screenshot I took of my Windows 10 Start menu.
Here’s a screenshot I took of my college mac’s dock.
Research
https://en.wikipedia.org/wiki/Graphical_user_interface
https://www.computerhope.com/jargon/g/gui.htm