Apps themselves are not part of any iOS backup. Since the Apps already exist in Apple's cloud-based App Store, and can be redownloaded at will, it would be pointless to include gigabytes of App installers in a backup.
A backup only contains user data and settings. When you restore from backup, the Apps are either downloaded and reinstalled, or if using iTunes and you've kept local copies of installers in iTunes, they can be installed from those.
But it is not possible to "backup" actual iOS apps to iCloud or iTunes. As to what documents, data and settings get backed up those are spelled out in the links you've already been given, and in the explanations by others.
Basically, an iOS backup is an all or nothing affair. You enable backup to iCloud and it runs, or you enable backup (or encrypted backup) to iTunes and it runs. Within the limits of settings for iCloud backups on our device, and within iTunes, you have some, very limited, ability to customize a backup. That's it though.