Welcome to the game.
You must have started the game at least once and log in to get the folders created.
They are normalle located at C:\users\<your windows username>\documents\Elder Scrolls Online\live\AddOns".
Please search this forum also with criteria like "steam" or "windows 10" or "onedrive" to get infos about problems with addons and OneDrive + Windows 10.
Manual addon installation
Extract the addon zip files here and check if the addon only builds ONE subfolder with the addonname. Extracting a filename called "myStatus" (where the ZIP archive contains the folder "myStatus" will normally create a subfolder "MyStatus" and put the archive contents (the folder "MyStatus") in there.. This is wrong!
The path needs to be something like "...\AddOns\MyStatus" and not "...\AddOns\MyStatus\MyStatus"
Minion
You could also try the addon update tool Minion:
http://minion.mmoui.com/
It is very easy to use and updates your addons, makes finding new ones easy too.