How to Add Categories to WordPress Posts
Categories can help you organize your WordPress content. Categories can also your visitors to find the content they're looking for.
In this video, Topher has a post called "Local Events Continue to Increase".
On the right-hand side of the post is a box called "Categories". By default, there is a category called "Uncategorized" because WordPress must have a category. It is possible to have child, nested categories. One example would be "Music" as a child category of "Events".
Click "Add New Category" and you can create new categories for your posts. If you assign your post to a new category, WordPress will show the new category when you view the post. Click "Categories" in your WordPress admin menu, and you can manage your site's categories.