Clone item that's not from the picture

1, Open the picture file  (A) with the object that you wish to add to another photo 

2. Use one of the selection tools, e.g. magnetic lasso or lasso tool, to select the object precisely. You should see an outline ("marching ants") once the selection is complete.

3.Go to Edit>copy

4. Open the target photo (B)

5. Go to Edit>paste

6. Activate the move tool and position A on B at the appropriate locus. A&B will be on separate layers.

Note: it is desirable to have the resolution of A&B the same value. Also the Brightness/contrast should be close so that the composite does not look fake.

.  .  .  Or you could tile the photos (using Window>Images>Tile) and Alt-click on the source photo and Click and drag on the target photo with the Clone Stamp tool.

If the item is a photo, open it in PSE and drag the photo to the image, and it will appear as a layer.