Posts vs Pages
There are two main types of content on your WordPress website, posts and pages.
Posts are blog posts, they often display their publish date, author, feature image, and can have comments. They are often displayed in an "archive" (like on a blog) where the newest post is at the top of the list, and the oldest is at the bottom.
Posts can also have categories and tags, which allow your readers to see an "archive" of all posts within a certain category or tag.
Posts are edited with the default WordPress Blocks Editor whereas pages have the additional option of using the Page Builder.
Pages are what form the website's structure.
Usually, there is a home page, an about page, and a contact page, but you can add any other pages you need. Pages are also used for "endpoints" such as "Subscription Confirmed" or "Thanks for your purchase".
Pages can also be used for things like registration forms, carts, checkout, and account details.
Pages have the option of being edited with the Page Builder, which gives additional options for layouts.
It's also worth mentioning the difference between post layouts and page layouts.
The posts on your website usually share the same layout. The content for each post is not managed by the page builder, it's managed instead in the Posts section of your website. Posts are usually written like articles, updates, announcements, etc...
Since pages usually exist for their own unique reasons (about, sales, confirmation, registration, etc...), we use the Page Builder to build custom layouts for each page. Of course, some pages will share the same simple layout, but main pages like your home page usually have a completely unique design to meet it's goal of welcoming your readers.
Your website menu is made up of pages, whereas your blog is made up of posts.