How to update JFrame Label within a Thread? - Java

I have tried a lot, but can't seem to get it to work.

I was told to use EDT with the following example.

    SwingUtilities.invokeLater(new Runnable() {
        public void run() {
            //  Modify the GUI here
        }
});

I have read on this topic a lot and still don't understand. I get what a thread is, but the .invokeLater still makes no sense to me. Honestly if you can explain in detail this it would be a big help!

Goal of Program: To get the randomly generated key that is constantly created every second to update itself afterward in the GUI.