If you’re an Apple user, chances are high you’re already connected to iCloud. If you’re new to Apple, you should know that iCloud is a mostly invisible, but important, set of services designed to keep documents and data in sync and current between Apple devices. That means, for example, that if you update contact information on the iPhone, the change gets pushed to all your Macs, iPads, iPod touch devices — any Apple device logged into the same iCloud ID.
iCloud storage, backups and pricing
Beyond simple data syncing, iCloud is used for storage, similar to DropBox or Microsoft’s OneDrive. You can upload, share and store documents and data and then access the docs and data from any computer with a web browser. iCloud is also used to store and transfer large attachments sent from Apple’s iCloud email addresses.
Source: Computer World – All Content