Hello-
There are a number of functions for these devices depending on the mode being used. The User's Manual (http://www.ni.com/pdf/manuals/320504c.pdf) describes these functions in detail in chapters 4 and 6 for S and G mode, respectively.
There are also commands for the actual instrument as well. An example would be *idn? for most GPIB devices. See the manual listed above on how to send these commands to the instrument.
Randy Solomonson
Application Engineer
National Instruments