Keurig It definitely can be confusing the first time!
You only need 2 pieces: Cheogram app and jmp.chat number.
jmp.chat is a VOIP service that gives you a phone number and acts like a bridge between traditional telephone network and Jabber network (also called XMPP). You pay the company behind jmp.chat for the phone number and SMS/calling services. They "convert" traditional SMS and calls into instant messages and VOIP calls via Jabber.
To receive and send messages and receive and make calls you need a Jabber client app. Cheorgam is one of such apps, the benefit of this particular one is it was made by the same team as jmp.chat and works very well together.
The best way to start is pick a phone number on jmp.chat homepage and they will walk you through the process.