Hi, Please take example from home page where the sidebar is always visible. The inner page's include the categories dropdown in header.
So include the header without categories dropdown as in home page of our demo. Then create a sidebar.php to display sidebar in left side and use php <?php require_once to include sidebar.
The code structure can be like below.
<?php
//Header.php
//Includes everything starts from <html to <body and also the header code.
// header.php also includes <div class="container">
//Container will be closed in footer.php
require_once("header.php");
//Sidebar Column
//Sidebar div start and ends in this file
// Sidebar also contain a widget for categories.
require_once("sidebar.php");
//starting div for content and closing inside all content.
require_once("content.php");
//Includes closing div for container which we started in header.php
//closeing of body and html tags as well and other footer elements.
require_once("footer.php");