[Minimal] Within the product description editor, or the page editor, switch to the HTML view by clicking on "View HTML" at the top right. You then need to use the following code, while taking note of the instructions in the comments.

gistfile1.html

<!-- This is your tab navigation -->
<ul class="tabs">
  <li><a class="active" href="#tab1">Sample Tab One</a></li>
  <!-- The key here is that the href ID equals the <li> ID used below -->
  <li><a href="#tab2">Sample Tab Two</a></li>
  <li><a href="#tab3">Sample Tab Three</a></li>
</ul>
 
<!-- This is your tab content -->
<ul class="tabs-content">
  <li class="active" id="tab1">Tab one content goes here</li>
  <li id="tab2">Tab two content goes here</li>
  <li id="tab3">Tab three content goes here</li>
</ul>