You should clone (duplicate) the new editable pages that you have created if you want to use them later as templates. If you do not clone them, you might inadvertently overwrite them.
To clone a page, Go to:
Admin menu → Settings → Editable Pages → Identify the Page you want to Clone →
Click on Edit → Clone this Page → SAVE
If you want to learn how to use the Menu Manager in order to create new categories and subcategories in the main menu tab check out the following tutorial: “How to link the editable page to a menu or submenu ?”