WordPress allows you to create web pages using pages or posts. A WordPress page or post is a single web page. So what’s the difference?

Pages
Think of pages as permanent content which rarely changes. The site pages are the foundation of your WordPress website. This would be things like your homepage, about page or contact page. This is information which rarely changes.
Posts
Posts are always organised into groups or categories on a website. For example, a website on running might have several articles with tips on how to run 5K all grouped around the category “5K.” Posts are for pieces of content that need to be grouped or organised. Posts are organised in a number of ways. What can be confusing, is that WordPress automatically creates web pages by itself to help organise your content. These are known as archive pages.
Categories & Tags
Categories and Tags are used to help you organise your websites posts.
A great analogy taken from a book called ‘Learn WordPress Visually‘ is that it’s best to think of categories and tags as the way a book is organised. Categories are the chapters and Tags are the index terms. So a category for a post called “Sites to See in Edinburgh” would be “Edinburgh Things to Do” and the tags would be “National Gallery of Scotland” and “Edinburgh Castle.”
Every single post you create must feature a category. Tags are optional. I recommend using tags as search engines love being able to index your web pages, tags help with this.
You can have subcategories which create a hierarchical structure for your posts. This is beneficial for SEO purposes.
WordPress will automatically categorise posts by the date they are published and who wrote them. These are known as author and date archives.
Exercise:
By default, when you create a WordPress website, a standard category called “uncategorised” is automatically created. Rename this category to something useful and relevant to your website.