The tags for you story are edited under the “publish” button. Medium will fill in two of them, often correctly, sometimes very weirdly. You can remove those if you wish by clicking the ‘x’ in the upper right corner. To put a custom tag, just start writing whatever you like and either a list will pop up with the word you wanted (and how often it has been used on Medium) In the case the word you wanted is not on a list, just write it anyway then hit enter and you’ve just created a new tag. You can have up to 3 tags on your story.
When you want to submit a story for publishing, the trick is to not click ‘publish’ when you are done editing your tags but click the 3 dots next to the ‘publish’ button and chose “add to publication” The Weekly Knob should be in the list of publications you can submit to.
I don’t think it’s a stupid question, and I think I gave a correct answer, but then again I’ve only been an editor for 2 and a half weeks :) Maybe Your Friends @ Medium can weigh in on this?