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.