The code below will create a green link (Proteopedia's links that interact with applets are green) with the text 'Turn on labels' that will execute the script inside <script> and </script>
<jmol>
<jmolLink>
<script> select all; labels on; </script>
<text>Turn on labels</text>
</jmolLink>
</jmol>
Replacing 'jmolLink' by 'jmolButton' will draw a button.
<jmol>
<jmolButton>
<script> select all; labels off; </script>
<text>Turn off labels</text>
</jmolButton>
</jmol>