You can copy and paste selections using the Move tool or the Copy, Copy Merged, Cut, Paste, or Paste Into Selection commands in the Edit menu.
Keep in mind that when a selection or layer is pasted between photos with different resolutions, the pasted data retains its original pixel dimensions. This can make the pasted portion appear out of proportion to the new image. Use the Image > Resize > Image Size command to make the source and destination photos the same resolution before copying and pasting.
Selections that you cut or copy are stored in the Clipboard. Only one selection is stored in the Clipboard at a time.
When you exit Photoshop Elements, anything in the Clipboard is lost unless Export Clipboard is selected in the General Preferences.