Would like to learn from this plugin

Hi all,
I’m learning plugin development (How to Develop WordPress Plugins from OSTraining) and near the end of the course. I would like to learn more about a real life plugin here in the Plugin directory and since I am particularly interested in User Profiles and Registration etc. I thought this plugin would be a good example to learn from.

Unfortunately plugin training tutorials don’t really teach very advanced topics and how a complex plugin like this works, so I am a bit lost here looking at the code.

I would be very grateful if someone can point out where in the code I should start with learning how this plugin works. I’m not looking for hand holding but just need some helpful pointers and will look up the resources in the codex when required.

I how this is not a very stupid request and thanks in advance to anyone who helps out.