Hi madlock,
Thank you for posting in the Apple Support Communities. I see you have a few questions about how to use iCloud.
The toggle switches in the screenshot you sent determine which data you sync between iCloud and your devices. If you were to turn on Messages here, for example, it would then enable Messages in iCloud, which syncs your messages between devices much like it would with contacts or photos. The article Keep all your messages in iCloud has more about this specific feature for reference.
Regarding backups, iCloud and iTunes will only back up data that's not otherwise stored in iCloud. Using Messages as an example, if you were to leave it off in the screenshot you shared, your messages would be part of your backups. On the other hand, if you turned Messages in iCloud on, they would then be synced to iCloud and your other devices, and no longer part of your backups. This is a great resource if you'd like to learn more About backups for iOS devices and what they include.
You also mentioned including or excluding specific apps from backups. To do this, you'd tap Settings > [your name] > iCloud > Backups. Then, tap the device you're using and scroll down a bit. From there, you can toggle apps on or off to decide if you want them to be part of the backup: Manage your iCloud storage.
The links I provided above have some excellent information, and this is another great resource you might check out: iCloud Support.
Hopefully this helps to answer your question.
Have a great night!
