How do I create a simple drop menu for/on a mobile app?

[Chappie]

Hello.

Could I please just ask, how I would go about creating a simple drop menu for a mobile app?

Working with an html template, the coding for the bottom bar, has 3 options. One is home, second is a menu (i've included below), and the third is a search button.

I'm just working on the menu button:-

<!-- mobile bottom bar -->
<div class="mobile_bottombar d-block d-lg-none">
        <div class="header_icon">
                 <a href="javascript:void(0)" class="icon_wrp text-center open_category" id="mobile_menwrap">
                           <span class="icon">
                                  <i class="icon-list-ul"></i>
                           </span>
                          <span class="icon_text">Menu</span>
                   </a>
         </div>
 </div>

I'd be grateful if anyone knows how to create a simple drop menu.

Thank You.