blog.liquid template is used to render the blog page. The primary purpose of this page is to list the articles within a blog.
Filter a Blog by Tag
You can use article tags to filter a blog into smaller subsets of articles. For example, if you are on the blog page and want to only show articles with the tag news, you can do so by appending the tag's handle to the end of the collection's URL.
This can be used to set up subcategories in blogs.