How you can add custom fields to you WordPress Theme.

custom-field.php

<?php
if(!function_exists('spx_custom_field')){
  function spx_custom_field($attr){
    global $post;
    $name = $attr['name'];
    if(empty($name)) return;
    return get_post_meta( $post->ID, $name, true );
  }
}
add_shortcode('new_field','spx_custom_field');