What exactly do Civil Affairs 38B do?

As you can see, there are many answers to your question. The Special Operations Recruiting Battalion will be your best source of info. sorbrecruiting.com
Reserve CA and Active CA do the same thing, and they also don't. You are active, so you would go through the entire pipeline which can get almost 2 years long if you are chosen to become a Special Operations Combat Medic (SOCM) along with CA. Language is sometimes allowed to be picked, and sometimes skipped if you are a native speaker AND a SOCM AND have a degree. Those decisions are completely up to cadre, proponency, and the Commandant. Deployments are quite often, but shorter than the usual combat deployments. Countries are many, your travels will be to places you didn't even think the Army was working in. Yes, you will need to go to jump school, and be expected to eventually become a Jumpmaster.

As for my definition/what I can say about CA. CA influences Diplomatic, Information, Military, Economic, Financial, Intelligence, and Law Enforcement (DIMEFIL) sources of national power. We fight battles with words and actions, and sometimes do not even carry weapons. We can be confused for PsyOps but we are very different (its just hard to explain). We work with embassies, other SOCOM units, and even alone. Some people believe that CA is all teddy bears, soccer balls, and hugs. While soccer balls have been used, sigh, it is not what we do! CA is not the Peace Corps!!!! We probably miss out on a lot of good soldiers because they think we just do nice things, but then again perhaps a closed minded person isn't what is needed in this job.

It is a job that requires lots of critical thinking, problem solving, and creativity. Civil Affairs Assessment and Selection is no joke, and will test your physical and mental prowess. I love the job. It is the best deployment you could ask for, most fun, and most independent you could be from the flagpole's. Contact the SORB, talk to more actual CA people, look at historic CA/CIVMIL from Vietnam and Japan, and make an informed decision about your career, you are at a great rank to switch over, you'll get tons of team time!

As a Reservist. Deployed: Get a list of villages to turn friendly, setup meetings with elders. Enjoy delicious food with elders and whoever else he brings, talk about how to help the community and what they need. Get needs, go back to base and make a plan within your budget. Get budget approved, hire contractors, get projects built. Enjoy applause from locals for helping them out. Move on to next village. Assuming you're in a bad area you won't be able to do anything but fight.

At Reserve center when not deployed: Sit around and do nothing but watch powerpoints or listen to pointless training that means nothing once a deployment has started. Watch everyone take themselves crazy amounts of seriously while walking around the reserve center for 1 weekend a month. Laugh. Wait for deployment, go to a school every now and then. Try not to lose your civilian career.

The best way I have ever had it stated to me (8 years as a 38B) was that we build exploitable relationships. Not in the intel sense, but in the we need a favor sense. We make friends with the politicians so that if we need to get permission to work with the local population they'll work with us; we make friends with the clinic doctors in case we want them to conduct health and welfare training for the civilians; we make friends with International Organizations, Non-Governmental Organizations, etc. in case we need someone to provide whatever resources are needed. We essentially are the link between the military and anything civilian, or on occasion host government military.

The level we conduct at is entirely dependent on the commander's understanding of the scope of abilities Civil Affairs encompasses, and the competency of your Civil Affairs company. A jacked up CA unit can screw up a situation faster than an excellent one can fix it.