Might be better if you can do a screen shot this way John.
Either use your screen shot tool in gimp (Under create > screenshot) or, ctrl Prt scr on your keyboard then paste as a new image into gimp. I usually do the latter as have found it to be quicker.
After pasting your screenshot crop it down to what you want to show.
Usually to help others help you make sure your gimp tools and tool options are showing maybe also your layer dialog.
Then save it as a png and upload as a file
Either use your screen shot tool in gimp (Under create > screenshot) or, ctrl Prt scr on your keyboard then paste as a new image into gimp. I usually do the latter as have found it to be quicker.
After pasting your screenshot crop it down to what you want to show.
Usually to help others help you make sure your gimp tools and tool options are showing maybe also your layer dialog.
Then save it as a png and upload as a file