Create a new template
Just create a new directory at includes/sts_templates/ and put template files in it.

Template Files
sts_template.html : the main template file for all pages.
index.php_0.html : template for home page.
product_info.php.html : template for product_info.
boxes/ : infobox template (need enable the “Use template for inforboxes” in admin), these files are php files.
boxes/infobox.php.html : general infobox template.
content/ : contents template (need enable the Product Info module).

boxes/infobox_boxname_php.html : individual infoboxes template. boxname can be:
best_sellers
categories
currencies
information
languages
manufacturers
new_products
reviews
search
specials
shopping_cart
whats_new

Placeholders
$sid : osCsid=xxx
$templatedir : Contains the path to the template folder, without trailing slash.
$urlcataloglogo: link to index.php
$cataloglogo : Shop logo with link to index.php
$urlcartcontents: url for shopping_cart.php page

Infoboxes:
$bestsellersbox
$cartbox
$categorybox
$catmenu
$currenciesbox
$informationbox
$languagebox
$maininfobox
$manufacturerbox
$orderhistorybox
$reviewsbox
$searchbox
$specialbox
$tellafriendbox
$whatsnewbox

Placeholders for product_info
$startform
$productname
$product_popup
$productsid
$regularprice
$specialprice
$productmodel
$imagesmall
$imagelarge
$productdesc
$optionheader
$optionnames
$optionchoices
$reviews
$moreinfolabel
$moreinfourl
$productdatelabel
$productdate
$reviewsurl
$reviewsbutton
$addtocartbutton
$endform
$alsopurchased

Adding new variable
Adding new variable in includes/modules/sts_inc/sts_user_code.php, such as:

$sts->template['custom_build'] = ‘<a href=”‘ . tep_href_link($link_file, $edit_params, ‘SSL’) . ‘” class=”headerNavigation”>’ . HEADER_TITLE_CUSTOM_BUILD . ‘</a>’;

And then you can use $custom_build in template.