iCloud & iCloud Photos · iCloud storage space and plans
What's the difference between iCloud and iCloud+?
Short answer: iCloud is the free service with a small amount of storage; iCloud+ is Apple's paid plan with more storage and extras like Hide My Email, custom email domains and family sharing of storage. Storage Studio works the same with either.
iCloud is the free service every Apple Account gets, with a small amount of storage. iCloud+ is Apple's paid subscription: more storage, plus extra features such as Hide My Email, custom email domains and HomeKit Secure Video support, and the option to share your storage with family. Apple's own pages list the current plans and features.
Storage Studio doesn't depend on which you have — it frees space on your Mac either way. See whether to choose iCloud or an external drive.