Hi everybody!
I would have liked to have responded quite a bit sooner, but all your ideas and suggestions required me to do quite a bit (a lot, to be honest...) of extra studying into your suggestions. Thank you all very much for the pointers.
My level of understanding caused me to end up selecting the stuff that I wanted to make transparent (delete) with the Magic Wand, not choosing any subtract or add option in the tools to the left of the Tolerance sliding bar in the menu at the top, but leaving it at the default setting (Replace), and sliding the Tolerance bar up and down until I was happy with the amount of stuff selected. I then simply hit Delete on the Keypad.
I then used the Lasso tool to select the stuff that had not been deleted and hit Delete every time that I'd lassoed an area - until everything had been deleted, or cleared as it were.
I initially saved the result as a JPG file, only to realize that I needed to save it as a PNG file for the deleted area to show up clear.
Well, for now, I am chuffed with myself! It is a really difficult piece with lots and lots of colours that need to be deleted in the background, but which are also found in the actual stuff that need to stay.
But, thanks to your kind help and guidance I now have what I wanted to have!
Here's to maybe even being able to help somebody else some day in the not too distant future!
Kindest possible regards
Inge