Greetings and salutations!
There's nothing profound about an address string. Usually it's just a single character representing the address of the instrument you're talking to. You might just try the GPIB communicate example vi's to familiarize yourself. Also, in the labview MAX interface, there is a "communicate with your instrument" function.
Good luck!
Eric
Eric P. Nichols
P.O. Box 56235
North Pole, AK 99705