title: Wordpress - radio button checkout woocommerce show/hide required field
body: <p>I'm Italian (sorry for my english) and I'm not a programmer.</p>
  
  <p>I need to insert in my checkout woocommerce site, a radio button with two options to answer this question: "Sei un privato cittadino, un'azienda o un libero professionista?".
  These are the options:
  1) Privato cittadino
  2) Azienda o libero professionista</p>
  
  <p>When users click on the first option, it has to show a required field: "codice fiscale". When users click on the second option, it has to show two required fields: "P.Iva" and "Ragione sociale". I've created the radio field with this code in form-billing.php:</p>
  
  <pre><code>    &lt;div class="woocommerce-billing-fields"&gt;
      &lt;?php if ( wc_ship_to_billing_address_only() &amp;&amp; WC()-&gt;cart-&gt;needs_shipping() ) : ?&gt;
  
          &lt;h3&gt;&lt;?php _e( 'Billing &amp;amp; Shipping', 'woocommerce' ); ?&gt;&lt;/h3&gt;
  
      &lt;?php else : ?&gt;
  
          &lt;h3&gt;&lt;?php _e( 'Billing Details', 'woocommerce' ); ?&gt;&lt;/h3&gt;
  &lt;?
  if($key=='billing_first_name')
  {
  ?&gt;
  &lt;p&gt;Sei un privato cittadino, un'azienda o un libero professionista?&lt;/p&gt;
  &lt;input type="radio" name="choice" value="privato_cittadino"&gt;Privato cittadino
  &lt;input type="radio" name="choice" value="azienda_professionista"&gt;Azienda o libero professionista&lt;br&gt;
  &lt;?
  }
  ?&gt;
      &lt;?php endif; ?&gt;
  </code></pre>
  
  <p>It works properly, but now I don't know how can I create the required fields like I described.
  Can you help me step by step? Please, consider I'm not a programmer. </p>