What is the difference between a blog post and a page?

Am I correct that in general, a page is static. It's information that I want to have always visible and readily accessible. I can list a page in a dropdown menu.

A blog is more dynamic. A post is not added to a dropdown menu and therefore may not be visible on the site if many posts were added afterwards.

For the vast majority of my site, which is largely research articles I have written, I want them always available in dropdown menus. These should then be pages, correct?

My ramblings and personal insights, which are really not important and only mildly entertaining are more suited to a blog, correct?

If this is the case, what is a category in a blog and what purpose does it serve? I've tried adding a few blog posts and giving them categories, but I don't see where assigning a category has done anything. It certainly doesn't seem to sort the blogs by topic.