To tell your theme what should be rendered as your main navigation, we need to setup a menu in Wordpress and assign it as our main navigation.
First of all, you need to create a new menu and add your menu items. For detailed instructions, see the WordPress documentation. In this example we add all existing pages by default and remove one that we do not want.
Now we just need to select the freshly created menu to be used as the main navigation on our site.
Menu on small devices
The default menu will be hidden on small devices. You can and should use the offcanvas position to have a mobile friendly version of your menu. The offcanvas element can be toggled from a menu icon. You can also publish other widgets in this position, but a menu is the most likey thing you'll want in any case.
Menus in any position and menu styles
You can create any number of menus you like and publish them as a Custom Menu widget in the Widget area of the Wordpress backend. You can assign that widget to any position you like.
There are three different menu styles, the Mega dropdown menu as a main menu, the Accordion menu in sidebars and the Line menu in the toolbar or footer. MValeo automatically styles the menu according the position it is published in.