The project was basically about using anthropologists and other social scientists to develop maps of the local population showing attitudes and loyalties. This is pretty standard stuff for marketing researchers. Want to put a new fast food outlet somewhere? Call in the market research experts to build and study maps showing who (in terms of what they eat and where they prefer to eat it) live there and what food outlets are already there. The military applications are more concerned with identifying the "opinion leaders." This is another marketing innovation, based on the idea that it's more effective to pitch the few people who most influence everyone else than it is to try and reach everyone with your message.
Up to 31 Human Terrain Teams (of 5-8 people) were in action at one. Each team usually contained one person who spoke the local language, and that enabled commanders to get a briefing from someone who is just a bit closer to the locals. Some of the teams had military reservists (who also have the necessary academic or professional credentials) but were from universities. This has caused much static in academia, where working for the Department of Defense is frowned upon. But these same academics often work for commercial firms doing the same work and many of them see no difference. Alas, those who did sign on for the Human Terrain Teams never heard the end of it from their academic critics. This despite the fact that many were attracted by patriotic attitudes or simply a rare opportunity to do research in a war zone. Most of those recruited were simply in it for the money and often did second rate work by working the system for all they could make. That experience can provide material for articles or even books.