Viber is an application developed by the Israeli-based company Viber Out in 2010. In 2014, it was purchased by the Japanese multinational company called Rakuten and is currently being operated by them. It is available for mobiles and desktop PCs for free downloaded. It has multiple usages, such as making calls and sending texts.
One of Viber's primary features is making calls.
Open the application.
Go to the calls option in the middle below of the screen as shown in the picture.
You will go to your contact list. Touch any contact you like that is using the application
As you can see, you can either call or send messages for free.
Now start messaging and calling.