iCLOUD.com VS iCloud on IOS and iCloud on mac
nevermind the iCloud on mac 🖥 I do not own a mac 🖥 yet but explain the difference for iCloud on IOS
iPhone 6, iOS 12
You can set up iCloud on your iPhone to sync selected things (e.g., files, Photos, Contacts, etc) with iCloud. You can continue to maintain (add, edit, view, delete) those things from your phone the same way as always. See: Set up iCloud on all your devices - Apple Support
You can also use any internet browser and log into www.icloud.com and access most of those things from the browser. Any changes you make from the browser will sync with the phone (and any other devices where you have iCloud turned on) and any changes you make from the phone will sync with iCloud.
Also see: Introduction to iCloud - Apple Support
If you are posting a question on this community, if the question is about using iCloud on your iPhone it would be better to choose the "iCloud on iOS" option in your screenshot. If you are asking about using iCloud in an internet browser it would be better to choose the "iCloud.com" option