That's a simple button. Have a look here on how to use it:
To understand how it works and how it can be adapted to your needs, look here:
https://www.gpsoft.com.au/help/opus12/index.html#!Documents/Codes_for_passing_paths.htm
https://www.gpsoft.com.au/help/opus12/index.html#!Documents/Codes_for_passing_filenames.htm