Just installed iCloud but can't upload data

I have set up iCloud on my Mac, downloaded it to my PC, and gone through the drill of choosing iCloud (in the little window where the options iCloud Drive, Photos, Contacts etc., and Bookmarks are checked. However, when I look in the side bar of my Windows Explorer (I have Win 7), I find no entry listed there for iCloud, even though the iCloud instructions say one should be there. All I find - not in the side bar but in the wide area to the right of Windows Explorer containing icons of my disc drives and other devices - is an icon named 'iCloud Photos', but I've not been able to upload anything that way, either. Anyway, it's mainly other data, not photos that I want to upload.

Furthermore, my Mac (OS 11 El Capitan) claims all I have to do is drag stuff there, but the window (in Safari) doesn't get out of full screen mode so I can't access anything to drag. I should mention that I'm a novice on the Mac, but experienced on the PC.