config.php or config.pinc are the global configuration files for TUTOS.
config_default.pinc is a exmaple file that is always read before reading config.p???. So you only have to change things that are different from the defaults and there is no need to copy everything (which will make problems when some usefull defaults are changed). Editing config_default is not a goot idea as it will be overwritten whenever you make an update.
The config files currently reside in [tutoshome]/php/ which is not the best place and may change in the future.