Is it really that hard to figure out what the rest does? Photos syncs photos. Safari syncs your browsing experience (bookmarks, reading lists, and tabs). Find my iPhone....finds your iPhone (if lost). Backup....backs up your device (daily and automatically). And Keychain syncs any saved passwords or credit cards you've used in Safari. Maybe with the exception of Keychain, everything else seems pretty self explanatory. And photos is still half baked for now since Apple hasn't yet released the counterpart app on the Mac.
iCloud Drive may be the only real ambiguous feature of iCloud at the moment as its not readily apparent on iOS as it is on the Mac. But it's basically just an online drive that syncs it's contents between your Mac and iOS device. On a Mac running Yosemite, it shows up just like any other drive or folder, on the left sidebar of any Finder window. But since iOS doesn't have Finder, iCloud Drive is only accessible within apps that so support it.