Thanks all of you [especially Pixey] for your patience and help.
I am now relatively proficient with the program after practising the techniques and pushing all the buttons.
The one thing that is not made clear, however, in any of the online 'tutorials' and it is the most fundamental aspect of understanding the principal of working with layers is that...... the layer you wish to work with should be 'selected' (highlighted) not just ticked or unticked in the box. I know this should be obvious and axiomatic to any proficient user, but at first it was the 'stumbling block' for me which was preventing my progression.
Thank you again for your help.