Register widget areas or sidebars in WordPress using register_sidebar() function

gistfile1.txt

<?php
/**
 * widgets_init action hook.
 * used to register, widgets or widget areas in a theme.
 */
add_action( 'widgets_init', 'oopthemes_widgets_init' );
function oopthemes_widgets_init() {
    register_sidebar( array(
        'name' => __( 'Primary Sidebar', 'theme-slug' ),
        'id' => 'sidebar-primary',
        'description' => __( 'Description of the Primary sidebar.', 'theme-slug' ),
        'before_widget' => '<aside id="%1$s" class="primary-widget widget %2$s">',
        'after_widget'  => '</aside>',
        'before_title'  => '<h2 class="widget-title">',
        'after_title'   => '</h2>',
    ));
}