Dropbox settings for syncing. I am officially confused.

Hello. This is my first attemt to get help here. 

I have an account which is as far asI I can detect something called Person Plus and i have 2 TB of space available. 

It is not a business and not a team or anything smart and complicated. It's just me, and it should be fairly simple. However, it's not. 

It is confusing.

There are no intuitive ways to figure out what is going on. i have triued to find answers, but all i can find is about how smart Selective Sync is and how smart Smart Sync is and nowhere is it explained how to disable Selective Sync or Smart Sync etc.
I have folders, that I can see on Dropbox web, but hey are not in my dropbox folder on the Mac. Yet, Dropbox says everything is synced. But it isn't.

I may have clicked a wrong spot somewhere, but on dropbox web I can't see the status of folders. And since they are not on my Mac, I can't see the status there either. Are they online only? Are they smart? Or selective? Or what? Why can't I see them on my Mac? 

In my dropbox folder on my Mac, I have created a folder named Online Only ... inb that folder I save stuff that should not take up space on my computer. It seems to work. Sorta. There are links the th files and folders that are online only, and as far as I can see, it's OK. I used to have 3 more folders in that Online Only folder, but for some reason they stopped working. Those were folders with files that are shared form out surveillance system (a different dropbox account that shares thjose files wit me and my wife's dropboxes - but as online only, so we only have links and not the full surveillance files). 4 of the 4 folders (from 3 of the four cameras) stopped syncing to my computer. So I have added them again, and now they are in my dropbox on the web (on level 1, that is NOT in the Online Only folder, so they should download to my computer - except they don't. Why is that?) My reason for having those 3 folders on the "root level" of dropbox was, that once they were there, I could move them to online only. But they do not download to my computer at all. I have tried to move them to the Online Only folder on dropbox/web, but again they do not show up in that folder on my computer. What to do?  can I reset the sharing preferences for those folders? Or what?     
How can I reset the syncing so the Online Only folder I have created is online only with links to the files and the rest is both on my computer and online?
How do I disable Smart Sync and Selective Sync if I have made mistake and clicked somewhere I shouldn't have? 
I also have an external harddisk and everytime I connect it, Dropbox starts making a backup. I don't want that. Where do I disable that backup?

Very confusing!