ajax, right way to do it and make it works?

In your functions.php file you should add an action to enqueue your scripts.

<?php
function my_enqueue_scripts() {
    wp_enqueue_script(
        'load_post', 
        get_template_directory_uri() . '/js/load_post.js', 
        array( 'jquery' ), 
        '1.0', 
        1
    );
    wp_localize_script( 
        'load_post', 
        'wp_ajax',
        array( 
            'url' => admin_url( 'admin-ajax.php' ), 
            'nonce' => wp_create_nonce( 'ajax_nonce' )
        )
    );
}
add_action( 'wp_enqueue_scripts', 'my_enqueue_scripts' );