The video calling feature is pretty self-explanatory, and functions much like WhatsApp's voice calls. If you try to start a video call with a contact bereft of the updated version, it will just process as a normal voice call, but it shouldn't be long before the wider community is brought up to speed.
It's clear that WhatsApp has been testing this feature in beta versions for Windows and Android in recent times. Those rocking the latest beta on Android should be able to get started right away. Android Police suggests that wiping the WhatsApp app data and logging back into the app thereafter may force activation of the video calling feature. Take this step at your own risk, though, and be sure to back up your chats first.
So, if you're on Android, at least, you can expect WhatsApp video calling to reach you very soon if it hasn't already. There's no word on Windows Phone or iPhone just yet, but it's reasonable to assume given the beta activity that each of the three major platforms will imminently see the face-to-face conferencing update.
Be sure to let us know in the comments whether you've been able to get up and running with video calls through WhatsApp.
source: Android Police