So the entry fields above are defined as:
INI Control
The name of the INI file.
Section
The name of the section.
Entry
The name of the entry.
The Control File is a standard format INI file.
For example, the settings above would be stored in a file called ProPath.INI.
The inside of the file looks like this:
[Data Paths]
FOLDER:MAINData=Path to the data folder
Important Note: when you select the option to use an External Control File, you will see the SYSTEM Path tab automatically appear. The Use a separate path for System data and INI files box will automatically be selected as well.
This is because you need to have a "point of origin" that tells ProPath WHERE to find the external control file.