Questions regarding Quickblox WebRTC in Android Studio

Hi everyone, I'm currently coding a project based on the Quickblox WebRTC. I'm using the code sample from here: http://quickblox.com/developers/Sample-webrtc-android

The code is opened in Android Studio 2.2.2 and it is able to run on my phone properly. However I encountered a roadblock in analyzing the codes.

Now let me start off with this, I'm not good at Android coding. I have never played with multiple module projects. I'm able to understand that different pages of the app are invoked from different modules. However I don't know how it works, I cannot find the master AndroidManifest that calls the pages.

I would also like to understand how the mutli-module project works, I have tried to Google it but I have no relevant answer so far. Thanks in advance.