The process of unpublishing a page makes it so that people are no longer able to see a page on the website or any of its content. Only the webmaster/owner of the site can see this page when logged in. It also removes it from the navigation and essentially makes it invisible to the public.
When using a website template, like the school templates, it is a good idea to not delete things like pages, web parts, etc. Instead of deleting a page, you can just unpublish a page and it will have the same impact where the public can't view it. That way, if at a later time, you want to re-enable the page again, it is all setup and ready to go.