Hi Christmas340,
Welcome to the Apple Community.
Your Apple ID is the account you use to access Apple services,
such as the App Store, Apple Music, iCloud, iMessage, FaceTime and more.
Apple support have articles online (links below) to help you:
How to change, add or remove Apple ID payment methods:
https://support.apple.com/en-us/HT201266
What is iCloud?
https://support.apple.com/en-au/guide/icloud/mm74e822f6de/icloud
You may want to check out:
iCloud Plans and Pricing
(When you sign up for iCloud, you will automatically get 5 GB of free storage)
https://support.apple.com/en-au/HT201238
Set up iCloud on all your devices
https://support.apple.com/en-au/guide/icloud/mmfc0f1e2a/icloud
What is iCloud storage?
https://support.apple.com/en-au/guide/icloud/mm7983cbca2a/icloud
Hope this helps you :)