So, why did they even bother creating a type of content called a Post? Isn't everything just a Page? Why did posts even come into existence in the first place? To answer that, we need to do a quick 1-minute flashback to the time, when the word "blog" came into being.
Did you know that the word "blog" is actually a short form for "Web Log" as in, a online log of events. Like a personal diary. On one of my web sites early in 2000 - a lot of web site owners did this - used to have a link in their menu called "Web Log". I certainly did, and it took the visitor to a page that had an online diary of sorts - the kind that we would publish on Facebook today.
A typical WordPress blog shows all of your blog Posts, in reverse chronological order. And if your blog is set to show the latest 5 posts, and you keep publishing new posts ever week, if I go to your blog in 2 months, I will see an entirely new set of blog posts on the front page, assuming your front page IS your blog. So if I am on your blog, and I like one of the posts I read on the home page, and I want to send the link to a friend, then I can't send my friend to just your home page, because depending on when the friend visits your home page, that post may or may not even be there. And so each post needed a more permanent link in order to be able to share with friends and index in search engines. That permanent link came to be known as the now famous "permalink" in WordPress.
Then, there is the WordPress Page, with a capital P, which is a more static entity. There's no rolling sequence of pages. A page is a page. It's just there. It has a link. Which is a permanent link.
So, when should you use WordPress Posts and when to use WordPress Pages?