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A template is not a page you can load directly. A template is used for the formatting (‘building’) of a ‘page’ (created via Page, Add) or ‘post’ (created via Post, Add).

On that page/post editing page, there is a place to specify the template that the WP will use when the page is output. There are default templates used (see Template Hierarchy) for posts/pages.

But you can’t call (load into your browser) a template file directly. The template file is sort of ‘output instructions’ that WP uses to build the actual page (or post).