To activate your menus, go to Appearance » Menus.

Create a menu by adding your selected pages to the right column on the screen, and order them as you want. Give the menu a name, save it, and then define a “location” for it clicking on the “Manage Locations” tab. The location you’ll need to supply at least right now is “Primary Menu”. Also, if you’d prefer it, as of WordPress 4.3 menus can be handled in the WordPress Customizer.