What is iCloud storage and backup?
When you sign up for iCloud, you automatically get 1 GB of free storage for app data and documents stored in iCloud.
If your iCloud storage runs low, you can delete files in iCloud Drive to increase your available space. See Delete files in iCloud Drive on iCloud.com for instructions about how to delete files on iCloud.com using a Mac or Windows computer.
To upgrade your storage, you need an iPhone, iPad, iPod touch, or Mac. See the Apple Support article Web-only access to iCloud.
If you set up iCloud on your iPhone, iPad, iPod touch, or Mac, you can also use iCloud to back up your iOS and iPadOS devices, including: photos and videos; device settings and app data; your iTunes Store, App Store, and Apple Books purchase histories; and more. See What is iCloud Backup?