FACE TIME
FaceTime is a video conferencing application developed by Apple, for devices running iOS or computers running Mac OS. It's look like Messenger or Whats App but it's deferent. It's for apple equipment. You can use it on Mac. If you have Mac and iPhone you can synchronised them like that you can make call with your Mac or iPhone. When you will receive FaceTime call you can respond with the Mac or iPhone.
How making call?
To make a call with FaceTime open the app
- click on New FaceTime.
- Add contact: your contact information can be their iCloud account or her phone number.
- Tap Audio or FaceTime. You can switch Audio to FaceTime and FaceTime to Audio
There is a step for making a call with FaceTime. At the end of call tap 
to end call.
