Apple iCloud explained: Features, setup, and benefits. Back up your data and use Keychain.

• iCloud is Apple's online file-sharing and backup solution for Apple devices.
• You get 5GB of storage for free, but many users upgrade to iCloud Plus.
• iCloud also includes Keychain, a password management solution.

iCloud is Apple's cloud storage service that lets you keep photos, files, and other data securely online, and accessible from any of your devices.

You can also use iCloud to back up your iPhone and iPad as well as share files with friends and family. You get 5GB of iCloud storage space for free. Admittedly, that's not very much online storage, but you can upgrade to iCloud Plus if you need more space.