A GUI Builder is a program that allows you to create your user interface by dragging and dropping components onto a display. The GUI Builder provides you with a palette of components and a design area. The palette of components contains all of the standard components (e.g., buttons, labels, text boxes). The design area is a window into which you can drag and drop components. The design area will eventually look like the window you want for you application. The GUI builder will then generate the code to that generates your window. You have to add the meaning to the window by processing button clicks, reading text fields, reading files, and placing the results in text areas, but you have avoided some the tedious programming involved with placing components on a JFrame.
Netbeans has a GUI builder that we use in Netbeans GUI Builer lab. We will learn the basics of the Netbeans GUI Builder and create a simple GUI with it.