I'm not a professional but am about to enter a program. The Human Factors and Ergonomics Society (HFES) webpage has been a great resource in telling me how to prepare for specific jobs and what they entail. I think it's under the "Career" or "Student" section. It's incredibly broad. You can come from engineering, computer science, psychology, maybe even anthropology. What you'll find yourself doing is making anything and everything easier and safer to use. This includes the Internet, cars, airplanes, toothbrushes...
You'll use cognitive psych to understand how and why we perform tasks and how to streamline them for consumer use. You could also be directly involved in the design process by creating prototypes (sketches, CAD) and performing usability tests, speaking/working with people about how to improve something and presenting the data.
A lot of it seems to be consulting but the government is a big employer for space programs and military use (how to make a drone easier to fly with less collateral damage) and web/tech industry is booming.