Layers - At last

I have never been a fan of layers, basically because I didn't understand how they worked. This has been going on for about 15 years, and probably extends from a rather poor tutorial in Amiga Format (Yep, a long time ago).
I decided that time had come to teach this old dog some new tricks, and thanks to some very useful tutorials online and a tool that seems capable of putting up with me (Gimp on OSX) - Et voila - My 1st piece of magic.
I have never edited a photo beyond pressing the "greyscale" button or resizing, so hopefully this is the beginning of many things to come.
If you can offer any useful hints, please let me know.
Thanks

James