Actually Jean, you can do that sort of selective editing quite easily without layers in a little freeware application called
Photofiltre.
Simply "draw" around the area you want to adjust using the Lasso tool and then select the required adjustment from the menu - Photofiltre applies the adjustment only to the lassoed area.
Just a thought, in case you find yourself struggling with layers. I use Photofiltre in this way for quick localised fixes all the time (toning down a "hot" patch on a bird's plumage or blurring a distracting background feature, for example).
I can be done and dusted in the time it takes for Photoshop or PaintShop Pro to open!
It's a very nice little editor for the more basic kinds of image processing.