If you want to add a post and have it be automatically added to a category, such as news, follow these instructions:

1) Click on Posts

2) Click on Add New

3) Add a Title

4) Add text

5) Add a category

6) If you have a News item on your menu and want this to be shown there, click News

7) Click Publish

Remember https://www.wpbeginner.com/beginners-guide/ has great tips and tricks for posting your blog.