Although there are many examples related to WebRTC based audio/video calls, specially browser based ones floating in the world wide net, but it is not always easy to conceptualize and implement the concepts when it comes to mobile devices.
Here is a step by step guide (mainly consisting the important steps) to follow through for a stable peer to peer call connecting mechanism for mobiles. This is a very high level diagram, and whoever following it has to have a basic idea of how WebRTC calls work and the basic terms like SDP offer and answer.