How to have a videoconference using WhatsApp (up to 4 people)

WhatsApp works great for videoconferences for up to 4 users. In my family we are using it a lot, getting connected at the same time my parents, my brother, my sister and I, with in laws and nieces and nephew. Somebody asked me how we do it, so I have prepared this short tutorial in case it is helpful to anybody. Cheers!