See "File IO" at
http://wpilib.screenstepslive.com/s/...e-2014-to-2015
You may need to use the base path /home/lvuser to write files to the roboRIO. Also, remember to use the Create Folder function BEFORE the Create File function if you are not sure that the folder has been created yet.
The File I/O functions are in the Programming\File I/O palette and the Create Folder function is in the Programming\File I/O\Advanced File Functions palette.
You can read and write to a simple text file or to your own binary file (as long as you keep track of the LabVIEW Data Type that the file uses). There is a subPalette that contains VIs for making .ini configuration files (caution: the configuration file is not actually saved until it is closed). Also, if you want to save a cluster of data in a human readable format, you can use the Flatten JSON or XML functions in the Programming\String\Flatten/Unflatten String palette.