I want to contribute to CodeIgniter!

[eluser]Narf[/eluser]
There is an application flow diagram in the docs that might help you: http://ellislab.com/codeigniter/user-gui...pflow.html
Also, there's a contribution guide on GitHub, although not related to the code logic: https://github.com/EllisLab/CodeIgniter/...ibuting.md

For the rest you will need to go through the code, there isn't any shortcut.