Hi there BugByte33,
It appears that you're planning to start using Apple devices, and you're trying to learn before you take the plunge. At the moment, you're wondering what types of things will use your iCloud storage, and we're glad to provide assistance.
Listen to music and more in the Apple Music app - Apple Support -- The only time iCloud is used for music is if you subscribe to Apple Music or iTunes Match. Even so, it doesn't count against your iCloud storage as you're only accessing the music found in iTunes that Apple has stored in the Sync Library.
iCloud User Guide - Apple Support -- iCloud is basically a syncing service. Instead of storing certain information on a device, it's relocated to iCloud and iCloud syncs the information to all of the Apple devices you use. The information you choose to sync will count as part of the storage being used.The Table of Contents provides a list of the information you're able to sync along with basic information on how to use iCloud.
Feel free to get back to us with any questions or problems you may have.
All the best.