DLL files are responsible for carrying out the majority of tasks on Windows-based systems. Therefore, it is essential to understand which DLL file contains which methods. This is very similar to the library files of Metasploit, which have various methods in them. To study Windows API calls, we have excellent resources at http://source.winehq.org/WineAPI/ and http://msdn.microsoft.com/en-us/library/windows/desktop/ff818516(v=vs.85).aspx. I recommend you explore a variety of API calls before proceeding further with creating RailGun scripts.
Refer to the following path to find out more about RailGun-supported DLL files: /usr/share/metasploit-framework/lib/rex/post/meterpreter/extensions/stdapi/railgun/def.
