Quote:I think it may be something to do with layers but I don't know how to use them. I've not found the correct tutorial for this yet. Hope someone can help without getting too technical.
I do not think you will find a tutorial anywhere that is particularly relevant. Your screenshot shows 19 layers but no layers dialogue. That is one of the hazards of rearranging docks, at least the tool options are showing.
What is the clone tool mode ? Off the screenshot below where it says 'Source' . That might have a bearing on the problem, however, more probably you are on a text layer rather than the base image layer.
Have a look at this https://youtu.be/EUVUJDZuyAs It might / might not help with the clone tool and proposes a different method. Not too long, duration about 3 minutes