From Forum Nokia Wiki

Before you write a line of code, it will help to understand the directory structure under which your source and project files should be stored. If you look at the example code accompanying your SDK, or use project wizards from an IDE to create a UI application, you’ll see examples of the typical layout used to organise a project.

A good directory layout is invaluable for keeping track of your code as the project grows. It’s usual to separate the project files, which will be described shortly, from the source code, which is itself split further into header files, such as .h and .hrh, and implementation files, such as .cpp. Resources, such as .bmp or .wav files used by the application, usually go into yet another separate directory. Test code should also be stored apart from production code.

Thus, a typical UI application would have the following directory structure and files.

data	Resource specification files (.rss)
gfx	Application resources such as bitmaps or audio files
group	Project files (e.g. MMP file and bld.inf)
inc	Header files (typically .h, .hrh and .inl)
src	Short for 'source', contains the implementation code in .cpp files
test	Test code