The CONFIG_PROP section is relatively new, and a lot of config files don't use it. The purpose of the CONFIG_PROP section is to specify which class is given control of what everything does. Most of the time, this is done by simply including a file from the ProffieOS/props directory in your config file, like this:
#ifdef CONFIG_PROP #include "../props/detonator.h" #endif
However, it would be perfectly fine to define your own prop class in this section and then define PROP_CLASS to be the name of your class. Learning how to do that is outside the scope of this tutorial though.
Here is a list of prop files that come with ProffieOS, each file will have some additional instructions at the top.