Dear Phil,
There are a number of ways that we can contact each other using free video calls. They include Facebook, Gmail, and WhatsApp. They all have relative advantages and disadvantages. WhatsApp is the best provided you already have it on your system.
1) Facebook has the advantage of giving the recipient a ring like it would be received using a landline. However both initiator and the recipient must have Facebook open on their systems for it to work. If this is not the case other means of communication would be necessary. An example would be sending an email asking if you want to chat and if so to open the Facebook. If I call, you would receive a ring and a box to accept the call. The system may ask you to authorize use of the microphone and camera. It also may ask you to sign in using your Facebook password.
If you want to initiate go into the Facebook openning screen. Close to the top is a horizontal menu with the "Messenger" icon. It looks like a speech balloon with a little "N" in it.