Let's say you're browsing the Web using Safari on your Mac and need to leave the house. If you pick up your iPhone or iPad, you'll notice an icon -- in this example, the Safari icon -- to the lower left on the Lock Screen. Swiping up on that icon will let you resume browsing on the same page. The process works the other way, too -- for example, if you started writing a document on your iPad, you can continue on your Mac precisely where you left off by clicking the leftmost icon in the Dock; the Handoff indicator appears immediately to the left of the Finder icon.
(If, for whatever reason, you don't want to use Handoff, you can disable it under System Preferences > General > Allow Handoff between this Mac and your other iCloud devices.)
iPhone integration: This is another great new ability If you receive a call on your iPhone, any Apple device with the same iCloud account and connected to the same Wi-Fi network will begin ringing as well, including the Mac. You can also dial numbers from webpages or Contacts using your Mac or your iPad; the device uses the iPhone to actually place the calls.
On the Mac, a call will display as an actionable notification stating the caller information -- such as the number or the contact picture and full name -- as well as the option to pick up the call or decline it. Next to the decline button, there's a drop-down arrow that will let you initiate a text conversation through messages if you'd rather not talk.
Pressing the Accept button will answer the call via the FaceTime app. Caller information will be displayed on a blurred overlay, complete with audio waveform and the options to mute, end and transfer the audio call to video.
Missed calls show up in the Notification Center. But I've gotta tell you: If you have multiple Apple devices, it's hard to miss a call. The iPhone 6 starts ringing, followed by the iPad, followed by the Mac and then the iPad Mini.
Instant Hotspot: Essentially, this allows the Mac to use the iPhone as a hotspot to access the Internet. No configuration at all is necessary -- if you have a recent iOS 8 device with a cellular connection, it will automatically show up under the Airport menu. Just select that and you're good to go.
AirDrop: This feature lets you transfer files to iOS devices from Macs and vice versa.
To transfer files from a Mac, use the Finder's AirDrop sidebar or any Share sheet, including the Share option prompted by right-click (or two-finger tap on a trackpad). Any device set to be discoverable -- Mac or iOS -- will be available.
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