Merging images with PSP IX?

I'm trying to learn how to blend images using PSP XI. It isn't going well. I can't get the images I'm using to blend...they are both titled by PSP as being "background" images, and when I try to copy and paste the selection of the second image that I want to merge into the first, it won't blend.

I'm trying to get this type of effect: 



Can anyone explain to me in really simple terms exactly what I need to do, step by step, to get the second image to not also be "background" so that I can merge it with the first? 

I deeply apologise if this has been posted before...I did have a look through the memories but couldn't really follow anything I found.