Combining two images side by side.
I recently post a side by side picture of my grandkids in their Halloween costumes and someone asked to explain how to do it.
I opened up both pictures in Photoshop Elements. I noted the height and width in pixels of the picture of the boys. Going over to the picture of the girls, I entered those dimensions in the appropriate spaces for the crop tool
Next I flipped over to the picture of the boys and chose Image, Resize, Canvas (not image). I entered a value of 2328 in Width, left relative unchecked and clicked on the left most arrow for Anchor. The picture of the boys was only 2323 wide but I used 2328 to leave a 5 pixel white space.)
Clicking OK gives me this
Now back to the picture of the girls, choose Select, All, then Edit, Copy. Back to the picture of the boys, choose Edit, Paste. Use the arrow keys to move the picture of the girls all the way to the right, leaving a thin white line in the middle.
The layers pallette looks like this
and the merged image like this