It is important to understand what Layers are and how they contain different image aspects.
There is a practical task in your Montage file, open that file and have a look at the original montage you first saved as a .PSD file, not the .JPG (Final) file, which does not have layers.
Open the .PSD file.
Make sure the layers window is open. Windows/Layers.
The Layers dialogue window below shows the Background and four layers. Each layer contains an image. If you have a layer that you want to delete, it's simply drag the layer into the rubbish bin bottom right.
If you need a new layer - select the icon at the bottom second right.
Should you need to duplicate a layer - Layer/Duplicate Layer.
Once you have completed your image and there are no more changes, you can save the finished image as a .JPG. But if you think you may need to make changes, or the image is incomplete, save the image as a .PSD, which can only be edited in Photoshop.
![](layers.JPG)
The image for the above as a .PSD and as a .JPG.