Template hierarchy
WordPress uses the query string to decide which template or set of templates should be used to display the page. The query string is information that is contained in the link to each part of your website. It comes after the initial question mark and may contain a number of parameters separated by ampersands.
See details and the hierarchy diagram here.
Template tags
Template tags are used within your blog’s Templates to display information dynamically or otherwise customize your blog, providing the tools to make it as individual and interesting as you are. Below is a list of the general user tags available in WordPress, sorted by function-specific category.