The Template
In the smarty template you need a button or a link to launch the modal.
Also in the template is the modal itself, which is initially hidden. It doesn't need to appear in the same place in the html as the link or button, it can be anywhere on the page. You may need to ajust the css and html to suit yourself, but this will get you started:
<a onclick="myModule_modal();" title="Open Modal">Open Modal</a>
<div id="myModal" class="search_box" style="display:none;">
<div style="float:right;">
<input type="button" class="simplemodal-close form_button" value="x">
</div>
<span class="title">Modal Title</span><br><br>
HERE IS THE MODAL CONTENT
<div class="clear"></div>
</div>