WordPress categories are a very easy way to group your posts. In wordpress category you can create parent and child categories making hierarchical arrangement of your posts possible
Create one post can be into more than one category. This helps to show the post exactly what you want. You can use the categories display them in widgets, menus or directly in your WordPress theme.
To creat new categories in WordPress, by choose Posts -> Categories page first.
On the left side of the page you will see a Add new category, in that you can create categories. Enter the category name, its slug (will be used in the category URLs) and click the Add New Category button. Here we created a category as Technology
After creating a category now, let’s make a sub-category of the Technology ad it named as Mobile. Enter a name and slug the way you did with the first category but this time select Technology posts as parent for the new category. Then, press Add New Category once more to save the new sub-category
After creating category structure, you can add posts to categories.
Open the new post or existing post. In the right side you can able to view the category tab. It allows to select the post category.
After selecting the category, click publish.