WordPress has it's own built-in Navigation Menus ('Menus'), configured using the Appearance > Menus option on the admin menu. The Scouting Challenge theme has its own built-in menu, the Navbar, but if you wish to use the WordPress Menus then that is fine. The theme has six Menu locations predefined and you may of course use the WordPress 'Custom Menu' widget in any of the theme's sidebars. The predefined locations are immediately before and after the calls to the optional Navbar at the top of the Header (referred to as the 'top of the page'), at the bottom of the Header, and at the top of the Footer and the theme will automatically load any Menus you create for those locations. These are 'as well as' and not 'instead of' the Navbar so you will need to disable the Navbar if you don't want it.
Limited styling for the Menus in the Header and Footer is included in the theme. They use the same class (navbar) as the Navbar so they are laid out the same, however there is currently no option to have fixed width buttons, only the variable ones. Also there is currently no option to change the background and hover colours. The background colours are set to Scout Purple for the one 'above' the optional Navbar and Scout Teal for the one 'below', with Scout Teal and Scout Purple being used for the hover colours. You are on your own with any Custom Menus you choose to use as there is no way to anticipate what you might want to do with them.
The six Navbars have the CSS IDs #bh_topofpage_prenav, #bh_topofpage_postnav, #bh_header_prenav, #bh_header_postnav, #bh_footer_prenav and #bh_footer_postnav and also have the class bhwpmenu which is not otherwise used by the theme. That should allow you to provide any styling you require.