In order to have your blog in a decent structure and ease your visitors' navigation throughout your posts and pages, you should categorize your posts.
Creating a new category
A new category can be created from the Posts menu > Categories.
Change the category of a post
In order to move a post from one category to another, you should click on Edit in the Posts menu, hover over the post you wish to edit and click Quick Edit.
From the Categories section select the new category (in our case the Test category) and click Update Post to save the change.
Delete a category
Note that deleting a category does not delete posts from that category. It will just set them back to the default category Uncategorized.