Here we will see how to enable Handoff on Apple Watch. Before we move on, Handoff is a feature of Apple Watch and iPhone. Using it you can start a task on one device and finish it on another.
For example, you might check email on your watch and then switch to your phone to compose a reply.
Like already said, it helps you to start performing a task on one device and finish it on another device. For Handoff to work, both the iPhone and Apple Watch need to be close proximity.
Now for an example, you open your mailbox on your Apple Watch. Then you open the email icon on your iPhone. Then you enter the phone passcode. Now the email that you were reading on your Apple Watch will be displayed on your iPhone. This is how Handoff works.How to Enable Handoff on Apple Watch December 22, 2015