Make default template two columns?

1. Add .php in wp-content/themes/

Write

<?php
/**
 * Template Name: <subpage-name>, left sidebar
 * Description: A one-colum template with left sidebar for <subpage-name> ONLY
 */
get_header(); ?>

2. Copy full-width page basic codes.

3. Add new div for

<div id="main" class="<subpage-name>-right clearfix" role="main">

                <?php while ( have_posts() ) : the_post(); ?>

                <?php get_template_part( 'content', 'page' ); ?>

                <?php comments_template( '', true ); ?>

                <?php endwhile; // end of the loop. ?>

            </div>
        <div id="main" class="<subpage-name>-left clearfix">
</div>

4. Set style in css.

div#main.<subpage-name>-left{width:240px;float:left;}
div#main.<subpage-name>-right{width:780px;float:right;}
article{margin-top: -44px;}