Apple introduced Continuity in Yosemite and iOS 8.1 to allow better handoff among devices for phone calls, text messages, browsing sessions, and hotspot use. Among its many requirements is that devices with which you want to use any of the connected have to be logged into the same iCloud account and, for most, on the same Wi-Fi network.
Readers have questions about the phone-call portion of Continuity, and there aren’t great answers for each.
Disabling FaceTime ringing
Ron Phelps would like his Mac to not ring on incoming iPhone calls.