Accidentally synced all my computer files to Dropbox

Hi. I have only been on the computer for a short time since we last communicated, so didn't read your message until now. I have the screenshot you wanted but it's late and I'll have to contact you tomorrow. I was poking around and saw the manage backups link, so I clicked it and the Mac backup was listed there with a delete option. I decided I had to try it and I clicked delete.  When I looked at my desktop all the things that had disappeared were back. And Mac isn't in my Dropbox folder. So maybe I fixed It?. I have no idea how the backup started in the first place so I'd like to prevent it from  automatically starting up again.