Template AKA Conditions
This settings will narrow where code will be executed.
By the default "All" is selected and this means that all pages will be effected by written code.
This option will unlock the section below to choose which single Page, Post, or even Custom post type you want to select to apply written code to it. Multiple selections are also allowed. There is no limit to how many single posts or pages you will apply code to.
This option will unlock the section below to choose with the post types group you want to apply the code to. For example, you can apply code to all Pages or Posts at once. If you have registered custom post types in this example "Portfolio" you can apply code to all Portfolio posts at once. Multiple selections are also allowed (posts, portfolios).
This option is a little different from the one above. This option will unlock the section below to choose with the taxonomies archive and not the group you want to apply the code to. Taxonomies are Categories, Tags, or custom registered ones (Portfolio Categories). Multiple selections are also allowed.
To explain it better if you select Categories code will be applied to the "Archive: Categories" page and not to posts that have categories.