Using Wordpress Categories
The best way to organize posts on your website is using WordPress categories. Your posts could be arranged in a hierarchical arrangement base on your parent and child categories. Also take note that a post could be in more than one category. This shows the flexibility of WordPress when it comes to how you want your site would look.
Login to your WordPress Site
You will see here all categories. Nothing is here if you have not created any category yet.
Assign Posts to Categories
Adding a category could be done on either creating a new post or editing an existing one.
Quick Tip: In selecting a category like the above image, its possible to also create a new category.