Moving / Copying pages
When in the edit mode, there are two options for saving the page being edited. These options are selected with the drop-down selector to the right of the "Page name:" entry.
Update / Move page (replace existing page)
If you have changed the name of name of the page by editing the "Page name:" entry, then the old page will be deleted and a new page created (move). If you have not changed the page name, the save page wll simply replace the old ome of the same name (update). This is the most common method.
Save as a new page (keep existing page)
Copies the content on the edit page to the page listed in the "Page name" box (copy). If you have not changed the page name, the content on the edit screen is added to the existing page, possibly duplicating information (append). This method would mainly be used to duplicate information or to split a page into two pages (save a copy & then delete the excess information form each page).
Keep in mind that these options will update the automatic menus, but will not alter any other links that have been made to these pages (i.e. links embedded in pages with the [page] tag).