Wordpress - radio button checkout woocommerce show/hide required field
<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>