All posts are going into one category

Hi. I am so immensely grateful for your amazing work. Nirvana is wonderful. Thank you so much. My only problem is that regardless of what category I add a post to, all of my posts go into one category from my menu. I’m not sure how to fix it. I tried deleting the category they were going into, but it didn’t delete and they remained in the category. Thank you very much for your time.