You can add a new post inside of category in WordPress. At first you need to add categories in WordPress before post. You can also add subcategory in WordPress. Lean easy to add categories and subcategories in your WordPress blog.
How to add categories in WordPress
1. Login your WordPress dashboard.
2. Move over your mouse pointer up to Posts and select Categories to add a new category in WordPress.

3. WordPress add new category page will open.
- Click below of Name and type your category name.
- Click below of Parent and choose this category parent if you have or keep it None.
- Scroll down below and click the Add New Category button to create a category on WordPress.

4. After that you will see recently created category on your WordPress category lists.
How to add subcategories inside of parent category in WordPress
1. Follow previous step to open your add new category page.
- Click behind of Name blank box and type your category name.
- Click behind of Parent and choose this category parent from lists.
- Click up to Add New Category button to add subcategories in WordPress.

2. You will see recently created category inside of your selected category.