1. Navigate to the ch5-post-source-link folder of the WordPress plugin directory of your development installation.
2. Open the ch5-post-source-link.php file in a code editor.
3. Add the following line of code to register a filter function to be called when the post and page content is prepared for display:

add_filter( 'the_content', 'ch5_psl_display_source_link' );

4. Add the following code section to provide an implementation for the ch5_psl_display_source_link function:

function ch5_psl_display_source_link ( $content ) { 
    $post_id = get_the_ID();
 
    if ( !empty( $post_id ) ) {
        if ( 'post' == get_post_type( $post_id ) ||
             'page' == get_post_type( $post_id ) ) {

            // Retrieve current source name and address for post 
            $post_source_name =
                get_post_meta( $post_id, 'post_source_name', 
                               true ); 
            $post_source_address =
                get_post_meta( $post_id, 'post_source_address', 
                               true ); 
 
            // Output information to browser 
            if ( !empty( $post_source_name ) && 
                 !empty( $post_source_address ) ) { 
                $content .= '<div class="source_link">Source: '; 
                $content .= '<a href="';
                $content .= esc_url( $post_source_address ); 
                $content .= '">' . esc_html( $post_source_name );
                $content .= '</a></div>';
            } 
        }
    }
    return $content;
} 

5. Save and close the plugin file.
6. Add source data to one of your site's posts and view it to see the new Source link displayed on the page.