I have seen videos where the author just created a category as a sub from the root alright, and yes, you could see it in the Main navigation bar. He also dragged it up or downward the directory tree and it would disappear from the main navigation and become an intem in the dropdown menu of other categories. Ok
Then I wanted to remove from sight some of the categories that were showing on the Main navigation menu.
I clicked on Do not display on the navigation menu. No effect.
I clicked on Active ? No
No effect. It would still show up in the navigation menu
I dragged it through the tree. No effect. Neither would it go away from the main navigation menu, nor would it become part of a dropdown. That is, nothing of what I was seeing in the tutorial videos.
I refresh the browser in all cases. I cant flush the cache because i dont have access to the System tab, but in any case, it was needed in the videos I watched.
I have made a 3 minute video on how the categories look like and their display settings and static blocks.
I dont have admin access so far, but would that make any difference ?
And last but not least: of course, the category I want to hide has a lot of products, it is not empty, but would that make any difference? I some categories with 2000 products, I suppose I am not going to have to deactivate each product before I can hide a category from the menu.
I am also seeing, I can create a new category. It will not show up in the Main menu. Do you have to be Administrator for that have effect? if yes, how come I can create categories even if they dont show? If I am not admin it should not even let me create the categories, regardless of whether they are displayed or not.
It look suspiciously like you forgot to clean cache. And if you don't have access to this functionality there's very little you can do.