You can also initiate a call from within a chat.
To do this, click the three dots icon in the top right-hand corner of the screen.
In the new window, you can create a new call by clicking the blue phone icon.
Once the call has connected, the timer will begin.
If you wanted to add another participant to the call, you can invite users by clicking the INVITE button on the right-hand side of the screen.
Now click the INVITE PEOPLE button, where you can now choose a contact that you wish to add.
You can search for a contact by typing their name.
Tap on the name of the contact, they are added to the call.