What exactly do I do in these steps?

4. copy the "tpl_header.php" from the template_default/common folder

You'll want to edit this file to incorporate your custom page-header. This is the appearance of the tops of all your pages.

5. copy the "tpl_footer.php" from the template_default/common folder

You can edit the footer area to appear as you like.

What do I really edit???

Thanks a bunch