Create custom widget area

sidebars.php

<?php
/**
 * Create custom sidebars.
 * Add this into your theme's php file where you want put all the custom 
 * widget area code.
 */
function my_register_sidebars() {

    /* Register the 'primary' sidebar. */
    register_sidebar(
        array(
            'id'            => 'after-page-content',
            'name'          => __( 'After Single Page Content' ),
            'description'   => __( 'This will shows widget after single page content.' ),
            'before_widget' => '<div id="%1$s" class="widget %2$s">',
            'after_widget'  => '</div>',
            'before_title'  => '<h3 class="widget-title">',
            'after_title'   => '</h3>',
        )
    );
    /* Repeat register_sidebar() code for additional sidebars. */

}

add_action( 'widgets_init', 'my_register_sidebars' );


/************************** Display on frontend ********************************/

/**
 * Add this where you want to display your widget area on frontend.
 */
if ( is_active_sidebar( 'after-page-content' ) ) {
  dynamic_sidebar( 'after-page-content' );
}