WiFi calling is a phone call, just like a regular phone call. As such, calls are made through a WiFi connection, it is called WiFi calling. With the help of WiFi calling, you can easily make phone calls without a SIM card.
If you are using the Oppo Reno8 Lite phone, you will also benefit from WiFi calling. You can contact your friends or other persons by enabling WiFi calls from phone settings. But the condition is that there should have a WiFi connection.