I know enough, not to be able to explain. >.<
Alright, I'll try. From what I know it works like this:
Win32API.new 'DLLFILENAME', 'METHODNAME', %w(INPUT_PARAMETER_TYPES), 'RETURN_TYPE'
So something like this here:
Win32API.new 'kernel32', 'GetPrivateProfileStringA', %w(p p p p l p), 'l'
would call kernel32.dll, the method called GetPrivateProfileStringA, sending inputs as pointer, pointer, pointer, pointer, integer, pointer and the return would be an integer (probably to test if the method was executed successfully). Keep in mind that a string is an object in RGSS, that means, you need to pass it through a pointer. Without knowing the specs of the method, you can hardly do anything. i.e. in this method the 4th string gets modified, but that's written in the documentation of the dll.