If you are not familiar with the BOS layout and apparently the passenger you are meeting is not, simply do the pick up at C and then both the passenger and you can follow the signs which direct you, in the first instance to B6 arrivals and then to the proper median. The passenger will see signs directing to the proper median (the furthest). Best to have them call you when they are actually standing at the median because you will be "moved along" in very short order.