Group image and rectangle selection

[Rakelle]

Still working on my greetings cards...on a file I've created which is 8in x 6in, I'm making a 4 x 6 card and attempting to copy what a lady did in a video, she was using Lightroom. She made a rectangle selection the size of the front side (4 × 6 in my case) then opened the image she wanted there, and aligned the image to the selection to get it centered (so far so good, and the best way I've found of centering the image so far) but then she GROUPS the image with the selection, and moves it into place to the right hand side of the file. I CANNOT for the life of me find a way of grouping them together in gimp. No matter what I search for i can't find a tutorial. 

Does this even make sence? 

[Ofnuts]

What is the "selection"? The selection mask, or the selected pixels in some layer?

You can move layers together in Gimp in two ways:

Click the chain link (empty space between the eye icon and the thumbnail) on all layers you want to move, and then move any of these with the move tool:

   

If your layers always have to be kept together, you can put them in a layer group, so you then just move the group

   

[Rakelle]

Thank you ofnuts, appreciate your help. I've abandoned that plan but your reply is still useful. Who knew that getting an image to print right would be such a huge issue. I will live to print another day..