Peakhandyman,
Big Ugly is right with his S-1 thru S-4 labels. There is however, in some units, particularily Special Operations, an S-5, which is Civil Affairs, but most likely NOT in this case.
2-6 IN stands for 2nd Battalion, 6th Infantry Regiment. They are a Regiment of Bradley Fighting Vehicles based in Baumholder Germany. At least they used to be. I'm not sure, but I'm thinking they have three companies, Alpha, Bravo, and Charlie, and of course the HHC (Headquarters and Headquarters Company).
The S-3 in this size Battalion will be a Captain, so I'm assuming your friend is a commissioned guy, yes?
As the S-3, he'll be in the HHC, and be a part of the Battalion Commanders Staff. He'll be "operations and training." The "S" folks are all staff guys. They basically make the Battalion run, and the Commander makes decisions based upon their input and suggestions.
Tell him to take care and come home soon.