There is two types of webpages: a blog post and a standalone page. A blog is usually time-dependent, you published it on a certain date therefore the filename must include a date (which can be any date since you can edit the published date using the date front matter tag); whereas a page is meant to be evergreen, so the filename does not have a date.
Another key difference is that blog posts are saved in the _posts directory and drafts are saved in the _drafts directory whereas pages are saved in any directory. The URL of a page will match the directory it is saved in. For instance, a page in the root directory will be example.com/page, a page in /documentation will be example.com/documentation/page. The URL can be overwritten using the permalink tag. Files and folders that begin with an underscore (_) are ignored when Jekyll builds your website. The _posts and _drafts folders are special. You can think of them has having a global permalink in _config.yml to take the filename and making a URL from it. For example, /_posts/2024-11-05-election-day.md will be converted to example.com/2024/11/05/election-day.