Hello Ariesx0,
When you subscribe to iCloud+ (or any monthly subscription with Apple), you are automatically billed until you cancel the subscription. To learn more about how the iCloud+ subscription works, look over this guide: Upgrade to iCloud+ - Apple Support. Specifically look at the last line of this page.
You're billed every month for iCloud+ unless you downgrade or cancel your plan. Each month you'll get an email to remind you of your upcoming payment.
If you subscribe to iCloud+ and want to cancel the service, follow the steps on this page: If you want to cancel a subscription from Apple - Apple Support.
For more information on what iCloud backups include, check out this link: What does iCloud back up? - Apple Support.
We hope this information helps you out.
Cheers!