Your Apple ID is an internet account that is used, amongst other things, to sign into, and access your personal iCloud storage space.
iCloud provides an optional @iCloud.com email address, cloud storage of contacts, calendars, notes, files (iCloud Drive), as well as a number of other features which are specific to Apple devices or apps.
In the course, Your Apple ID, and iCloud, we showed you how to sign in, and manage your iCloud settings, in System Preferences->Apple ID->iCloud.
But note that, those same iCloud settings can also be accessed in System Preferences->Internet Accounts.
In other words, Apple ID & iCloud fits Apple’s definition of an Internet Account. It’s given more prominence, because it has a number of additional features that are specific to Apple devices and apps.