Hi,
The first step is to install the GPIB hardware and drivers. I assume you have.
Connect the instrument to the GPIB interface, go to MAX (Measurement & Automation Explorer) and select "Scan for Instruments". If the instrument is detected, that means the the GPIB port can communicate with the instrument. MAX sends *IDN? to get the instrument ID.
Then, you need to get the command set for the instrument. This should be provided by the manufacturer. It is the set of commands that you can send through GPIB to control the instrument. Communication with GPIB devices is usually a query-response format, send a command (query) and get the response.
Hope this helps.
DiegoF
National Instruments.