How to learn about internal details of Open source projects

Open source is good place to learn , but many times we see that documentation is poor.

Mailing lists are great place to learn always but source code is one thing which speaks for itself.

I try to

Draw UML digrams

Draw API diagrams

Some of the free tools which i use i wanted to share

 

Want to read how to use yworks?

See it here

http://jugnu-life.blogspot.com.au/2013/02/generate-uml-diagrams-for-java-from.html

I found building javadocs for project using yworks uml plugin makes it easy to understand how things are flowing.

 

Read about using Apiviz here

 http://jugnu-life.blogspot.com.au/2013/02/api-diagrams-from-source.html

So after downloading source this is the first thing i do to make javadocs again to digg into the code

Want to have more fun ?

Read here

http://code.google.com/p/apiviz/#Sample

http://www.umlgraph.org/download.html

 

What are your ideas to learn in open source ?