Blog posts are managed here, separately from the site's pages.
A post is not a page
Posts have their own listing, their own addresses and their own archive. A page you build by hand does not appear in the blog, and a post does not appear among the pages.
A future publish date means not yet published
If a post's publish date is in the future it does not appear on the site until then — even when its status says published.
So "I published a post and it is not there" almost always means the date is ahead.
A post can have several authors
Authors come from the blog's own author list, not from admin users. That means a post can be credited to someone who has no account at all.
Categories and tags are defined elsewhere
Here you only choose them. Creating and editing categories, tags and authors happens in Blog Settings.