Handoff is a great new feature of Apple's forthcoming operating system, Yosemite. If you're not familiar with Handoff, it will allow you to start an activity (such as writing an email) on one device and continue it on another. Not all Macs will support it, though. Here's how to check if yours will.
Go to the Apple Menu, choose About this Mac, then click More Info, and then click on the System Report Head to the Apple Menu, then go About This Mac > More Info > System Report > Bluetooth. Look at the LMP Version. The version needs to be 0x6 for Handoff to work.
You can also access this information with a terminal command:
system_profiler SPBluetoothDataType | grep LMP