[ARIA] aria-describedby & aria-labelledby

When to use describedby:

For example you have a close button:

<button aria-describedby="closeReadable">X</button>
<p>Some kind of content</p>
<p id="closeReadable" class="visuallyHidden">Close this window</p>

When to use labelledby:

For example you have Billing section, inside you have address field. Just memtion address to the user, they won't understand, it is better to say "Billing address":

<h4 id="bukkubg_header">Billing </h4>

<label for ="form_address" id ="form_address">
  <input type="text" name="form_address" aria-labelledby="billing_header form_address" />
</label>