creating themes

[learnerabn]

Hi all,
I am a new bee to prestashop.
I want to build a new theme by my self.
when i started modifying the tpl file(as html files) i found lines like {if isset($meta_description) AND $meta_description}
I dont know where those variables like $meta_description coming from.
I there any template files located there?
how can i identify them?

Thanks in advance....

[rocky]

The meta-descriptions can be changed in the Back Office. Go to Preferences > Meta-tags to change the meta-description for index.php, 404.php, best-sales.php, contact-form.php, manufacturer.php, new-products.php, password.php, prices-drop.php, sitemap.php and supplier.php. Go to the Catalog tab and click the Edit icon next to a category to change its meta-description. Go to Tools > CMS and edit a CMS page to change its meta-description. When editing a product, click the "Click here to improve product's rank in search engines (SEO)" link above the short description to reveal the field to change the meta-description of the product.