To add additional tabs on the product detail page, you will need to alter the "product_detail.html" template. You can do this directly via the file in the "themes/YOURTHEME/" directory, where YOURTHEME is the name of the theme you are using, or you can do this in the "Settings" -> "Manage Templates" section of the admin area.
1. Open or select the "product_detail.html" template file.
2. Locate the following which displays the "Product Overview" tab:
<div class="tabbertab"> <h2>$lang[overv]</h2> <div>$product[full_desc]</div> </div>
3. Copy that code and place it where you would like you new tab to display, either before or after the "Product Overview" tab.
4. Change the $lang[overv] variable in your newly pasted code to the title you would like to display.
5. Change the $product[full_desc] variable in your newly pasted code to the content you would like to display in that new tab. Please keep in mind that if you would like to change the content dynamically based on the product being view, you will need to add additional PHP code in the global.php which we will not cover here.
6. Example of new code:
<div class="tabbertab"> <h2>My New Tab</h2> <div>This is what will fill the content area of my new tab.</div> </div>