I have a question for the photoshop masters here

I have a layered image at work and I want to add another image as a layer but i dont know how to do it. In this file there are like 4-5 images layers that were used as background images for a newsletter banner but i dont know how they added them to the file. Any ideas? Then there are more layers for text and some more to change the logo for new month and company logo. I try to do a screenshot tomorrow then it is more clear to you
