how do i see whats in icloud

See - Manage your iCloud storage - Apple Support.

I think the most complete way is to log into iCloud.com. You can use apps such as Photos to see which photos you have in there as opposed to just getting a general estimate based on category that you get from an iPhone. I think the only thing you won't see is how much is used for backups but you can always go to a mobile device for that.

In your iPhone go to Settings-> "your name" section -> iCloud. In that section you can see all your iCloud staff.