You can compare it with e-mail service. To be able to send and receive e-mails, you need an account from a provider.

It is the same with telephony (VoIP). You need an account from a VoIP provider. There are thousands over the world. So I can't tell you the one you have to chose. Select one with good rates.
From such provider you will get a server address (it is called "Proxy/Registrar" in PhonerLite) and a username and password.

Take a look here:
http://www.voip-list.com/voip_countries/

There are so many providers available - it depends on your needs. From what country are you from?

What is your definition of "free"? Nearly all providers offers accounts without any monthly fee. So if you don't call - you don't have to pay anything. Next fact is: If your called partner also uses VoIP (at the same provider), the call is free - you don't have to pay for it. Only if you call a landline or mobile phone you have to pay.
If your friends you want to call are using a special VoIP provider, you should also use that provider.

I don't know who is "they". But this is not the problem of PhonerLite.