responsibility of main sorurce files

I'm new fan of PostGIS. Could you help me for my starting?

May be due to the C language characteristics, the code isn't clear enough as C++. I'm puzzled with the function responsibilities of main sorurce files, such as lwgeom.c/legeom_api.c/lwgeom_functions_basic.c/lwgeom_functions_analytic.c and every LW*.c like lwline.c.   Are they have clearly responsibilities for everyone? Then i will know, a new funtion should put where.

Thanks!