That requires learning the various selection tools in Elements, then using them well. You could google 'selections in Photoshop Elements', or read the help system's overview of selection tools.
Since we're talking about googling for more information, often just learning the terminology for a given technique or tool can be helpful. The word to describe moving a part of an image onto another image (what you are asking about) is 'Compositing' or 'Composite'. Work that word into your google search and you're sure to find plenty of helpful hints on how to use the various selection tools. If you see a Photoshop tutorial, my guess would be that 80% of the tutorials involve selection tools or techniques that are in Elements, too; most tools (not all) are in both.
If you run into trouble and have a specific question, we're here to help.
-Mark
