Apple's iCloud acts as a storage, data-sync and back-up service for your iPhone, iPod touch or iPad. Through iCloud, iOS devices were finally freed from being accessories to Macs and PCs, because the likes of calendar events and contact data would be synchronised on-the-fly, rather than updated when you plugged your device in and synced.
But iCloud goes further than ensuring your appointments and phone numbers are up to date. Increasingly, other services rely on iCloud, including browser bookmarks, photo-sharing, app document sharing, and the means to find your device should you lose it. Additionally and perhaps most importantly iCloud enables you to keep your data safe, by backing it up to the cloud. This means that should your iPhone start going Vworp Vworp and mysteriously propel itself through time and space, like a mini-TARDIS (or, more mundanely, find itself smashed to bits in a puddle of muddy water when you drop it), you can restore your data from iCloud.
This walkthrough assumes you already have an Apple ID and that the thought of storing some of your data in the cloud doesn't make you want to don a tin-foil hat.
Not Enough Storage! Thanks, iCloud! But never fear: our walkthrough shows how to deal with such a problem.
1. Sign in
During the set-up of a new or upgraded device, you'll get the chance to sign in using your Apple ID and then to use iCloud. If you skip this step, you can still set-up iCloud on your device open the Settings app, and then select iCloud. In the iCloud window, type in your Apple ID and password and then tap Sign In. The device will most likely take a few seconds to verify your account.
2. Choose your services
You'll next be asked whether you want to merge the data already on your device with iCloud. This means, for example, if you've used your iPhone to enter some appointments in Calendar, these will then be sent to iCloud and made available on other devices signed into the same iCloud account. Again, it will take the device a short while to save this setting, so be patient while it does so.
3. Allow location services
You're next asked whether you allow iCloud to use the location of your device. Given that you control who else can see this, we recommend turning this feature on. At the very least, it enables you to discover the location of your device in the Find My iPhone app, should you lose it. Turning this feature on also means you can invite other people to see your location in the Find My Friends app.
4. Choose your services
By default, iCloud turns everything on, but you can tap the switches to turn specific options off if you don't want the associated data shared with iCloud, or if you have no use for the service. For example, if you want your Safari bookmarks to be device-specific and _not_ shared between devices, turn off Safari. Note that with Mail, iCloud sharing relates to an @icloud.com address and not all your email. Should you want other email to be readily accessible and synced across devices, investigate IMAP.
5. Start your back-up
Scroll down to and select Storage & Backup. Within, you'll see how much total storage space you have available on iCloud (5 GB free by default), and how much is available. iCloud back-up will be on by default, and will be triggered when the device is plugged-in, locked and on Wi-Fi. However, you can also manually start a back-up by tapping Back Up Now. Back-ups are incremental (as in, they only upload new data), but the first one may take some time.
6. Manage your back-ups
Depending on your iCloud usage, you may find Apple's 5 GB for free fills up pretty quickly. In fact, if you've existing back-ups in iCloud or too much data on a single device, you'll have to either cough up for more storage (tap Buy More Storage, select an option, and cover your ears to block your bank account's blood-curdling screams), or tap Manage Storage and select a back-up to edit.
7. Prune back-up data
On selecting a back-up, you'll (after a sometimes lengthy delay) in the Backup Options section see the data that's being stored, and how much space each app commands. Should you need to remove items, prioritise those that take up most space but that you can also easily restore from elsewhere. For example, Camera Roll images will be being saved to Photo Stream and downloaded into iPhoto if you have that connected to iCloud.
8. Back-up to iTunes
It's possible to restore a new or existing device from your iCloud back-up. New devices offer the choice during set-up; older ones can be deleted via Settings > General > Reset and tapping 'Erase all content and settings'; you can then opt to restore from a back-up during set-up. However, iCloud does occasionally go wrong. Therefore, also periodically back-up to your Mac or PC via iTunes. To do so, select your device, and in the Summary tab, click Back Up Now. The back-up may take some time.
9. iExplorer back-up
Occasionally, it's useful to back-up data from a specific app, thereby enabling you to restore it later (versus restoring an entire back-up); for example, you might have completed a massive game and want to free up space, but don't fancy the idea of some time in the future starting from scratch after a reinstall. Some games pull down saved data from iCloud, but most don't. Manual saves can be made using iExplorer. Connect your device to your Mac or PC and select Apps from the sidebar. Select the Documents and Library folders, Ctrl-click and export them to your computer. On a later app reinstall, these can be dragged back to reinstate your progress.
10. Reset iCloud or your back-up
If everything goes horribly wrong, take off and nuke the entire thing from orbit it's the only way to be sure. To do this, go to Settings > iCloud and tap Delete Account. The service will be removed from your device, and you can then start afresh. (Alternatively, if it's just your back-up that's gone a bit squiffy, go into Manage Storage, select your device and tap Delete Backup to remove it.)