iCloud is Apple’s take on cloud services, as the name implies. The service has many parts to it. But it’s free with any Apple ID.
Apple takes the privacy and security of its users very seriously. See this Apple support article for more info.
Sign in to iCloud.com from any Mac or PC via a web browser to access core apps and services such as Mail, Contacts, Calendar, Find My iPhone, and iWork for iCloud.
If you purchase music, movies, apps, books, or TV shows on one device, then iCloud can automatically and seamlessly push it to all your devices. In the background.
iCloud Photo Sharing
iCloud originally launched with a personal photo stream for everyone, so that photos taken with one device can be wirelessly pushed automatically to another device. In iOS 6, Apple added Shared Photo Streams, so that friends and family can share specific photos with specific people. Now in iOS 7, other people can contribute together to a Shared Stream; plus, Apple now allows you to share video via iCloud Photo Sharing.
Find My iPhone, iPad, iPod touch, or Mac
If a crook steals your Apple device, Find My iPhone, a service part of iCloud, can help you recover it.
You can lock it remotely or even wipe the device entirely to prevent data loss. And in iOS 7, if a thief tries to turn off Find My iPhone or wipes the device entirely, he or she will not be able to reactivate the device. With Activation Lock, your Apple ID email and password is required to reactivate the iOS device.
iWork and iCloud
iCloud automatically syncs all your iWork documents between all your devices. With iWork on Mac, iWork for iOS, and iWork for iCloud, no device is left out on the productivity.
Apps and iCloud
Apps on iOS and Mac can also sync your content between devices. Apps such as Pixelmator, GarageBand, Day One, and iA Writer sync your content seamlessly between devices; some apps even sync cross-platform, from iOS to Mac and vice versa.
Besides syncing your bookmarks, iCloud keeps track of tabs open across all your devices. Plus, it will even sync your Reading List web pages, so anything you need to catch up on is only a tap away.
For devices running iOS 7 or OS X Mavericks, internet logins, credit cards, and Wi-Fi networks and passwords can be seamlessly synced between all devices with maximum 256-bit AES encryption.
Mail, Contacts, Calendar, Notes, and Reminders
Keep all your emails, contacts, calendar events, notes, and reminders up to date on all your devices using iCloud.
Backup and Restore
You can now backup your iOS device to iCloud and restore your backup during set-up on a device. It’s completely wireless and seamless, and happens automatically every time you’re on Wi-Fi and plug in to charge.