Right. What DeadMeatXM2 said.... mostly. They are a little more flexable than that though. They don't always deploy from a helo... As DeadMeat said they are Para Rescue Jumpers, and really what that means is they are Rescue Specialists. The AF trains these guys to rescue anyone, anywhere, anytime. That includes from the tops of Everest/K2, the depths of the ocean, the most inhospitable extreme terrain, deserts, jungle, glacier, and all of this while under intense enemy fire, even hand to hand. They also deploy via all forms of parchute insertion, scuba, submarine, overland by motocycle, bicycle, FAV's, on foot, etc. They do often deploy with Combat Control Technicians, as DeadMeat said, but are actually self sufficient and can defend themselves and their patients in a firefight. CCT's usually have their own missions to attend to, and are incredible in their own right.
The highest trained, most elite units of the US SOCOM depend on PJ's all the time. Even Delta, and DEVGRU, who have their own medics will utilize PJ's during hostage rescue situations, allowing their own medics to focus on team members.
One thing they are known for strangely enough is possessing a quick wit, and a great sense of humor... I've known a few and they'll go all out to get a laugh. Total jokers. When I was a paramedic we learned to do the same thing, laughing helps people cope with tragedy. I guess that's something that comes natural to someone that makes a living pulling the good guys out of the worst of the worst, try not to dwell on the death and destruction, and get the job done.