On the official Bootstrap website at http://v4-alpha.getbootstrap.com/examples/, you can find an off-canvas example. The example will show you how to build a toggle able off-canvas navigation menu for use with Bootstrap. You can use an off-canvas side bar in your theme too. On the smaller viewports, a page with the off-canvas menu will look like that shown in the following screenshot:

When you click the Toggle nav button in the preceding page, the page content slides to the left and the side bar becomes visible.

The off-canvas menu use the template called template-offcanvas.php in the theme directory/ It should contain the following HTML and PHP code:

<?php 
/* 
Template Name: Off-canvas Side bar 
*/ 
?> 
 
<?php get_header(); ?> 
    <div class="container" id="content"> 
     
        <div id="inner-content" class="row row-offcanvas row-offcanvas-right"> 
     
            <main id="main...