Navbar Template

We add the .navbar directly under the opening body tag inside wp-content/themes/customtheme/index.php 

<nav class="navbar navbar-default">
  <div class="container-fluid">
      <div class="navbar-header">
          <button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#bs-example-navbar-collapse-1" aria-expanded="false">
              <span class="sr-only">Toggle navigation</span>
              <span class="icon-bar"></span>
              <span class="icon-bar"></span>
              <span class="icon-bar"></span>
          </button>
          <a class="navbar-brand" href="#">Brand</a>
      </div>
      <div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">
          <ul class="nav navbar-nav navbar-right">
              <li><a href="#">Link</a></li>
              <li><a href="#">Link</a></li>
          </ul>
      </div>
  </div><!-- .container-fluid -->
</nav>

The entire index.php file should now look like this:
 

<!doctype html>
<html <?php language_attributes(); ?>>
    <head>
        <meta charset="<?php bloginfo( 'charset' ); ?>" />
        <link rel="profile" href="http://gmpg.org/xfn/11" />
        <link rel="pingback" href="<?php bloginfo( 'pingback_url' ); ?>" />
        <?php if ( is_singular() && get_option( 'thread_comments' ) ) wp_enqueue_script( 'comment-reply' ); ?>
        <?php wp_head(); ?>
    </head>
    <body>
        <nav class="navbar navbar-default">
            <div class="container-fluid">
                <div class="navbar-header">
                    <button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#bs-example-navbar-collapse-1" aria-expanded="false">
                        <span class="sr-only">Toggle navigation</span>
                        <span class="icon-bar"></span>
                        <span class="icon-bar"></span>
                        <span class="icon-bar"></span>
                    </button>
                    <a class="navbar-brand" href="#">Brand</a>
                </div>
                <div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">
                    <ul class="nav navbar-nav navbar-right">
                        <li><a href="#">Link</a></li>
                        <li><a href="#">Link</a></li>
                    </ul>
                </div>
            </div><!-- .container-fluid -->
        </nav>
        <div class="jumbotron">
            <div class="container text-center">
                <h1>Welcome To Our Custom Site</h1>
            </div>
        </div>
        <div class="container">
            <?php if ( have_posts() ) : ?>
                <?php while ( have_posts() ) : the_post(); ?>
                    <h2>A single blog post.</h2>
                    <?php the_title(); ?>
                    <?php the_content(); ?>
                <?php endwhile; ?>
            <?php endif; ?>
        </div>
        <?php wp_footer(); ?>
    </body>
</html>

Complete and Continue