To open a picture you can go to file -> open and then select the picture you want to open. You can also do it through bridge (if you have it)a short-cut for it is control/command + o.
There are two ways, you can either click, drag, and drop the image into your workspace. Or you can go to File, Open, and select the image you want to add into your workspace.
You need to cut the part of the picture you want to use out of the original frame and paste it onto another background, or paste the picture onto another picture and then mask the parts you don't...
Photoshop Elements is Photoshop but with less features, so Photoshop is better but it is professional level software. For home use or to get started Photoshop Elements is OK.