By default, WordPress grab pages as your main menu. But you can create your own menu (Appearance >> Menus). Under this new menu, you can create menu items from posts, pages, links …etc., anything you want. You also sort (reorder) these items, even organize menu items into multiple levels. Finally, you can assign your own menu as the main menu. Please check “Navigation menus” for more details.
Furthermore, you can create as many menus as your want. The main menu can be different by each page/post. This can be done in the Themify Page/Post Options tab under each page/post editing screen.