When creating a post, make sure to assign it to a category. This improves website organization and functionality. The user is able to sort posts by category, which allows them to more easily find content relevant to what they are looking for. 

For the Classic Theme, posts that appear on the homepage must have an assigned category of Blog

Select the post you want to edit and find the Categories section, usually found in the right sidebar of the editor. Select which categories you would like to assign your post to. Posts can be assigned to more than one category. 

Click Update or Publish when finished.

You can also quickly assign a post to a category by hovering over its title in the Posts section of the WordPress dashboard and clicking Quick Edit.

Then, select the categories you want to assign and click Update when finished.