Hi, I am senior material research engineer at the NASA Glenn Research Center in Cleveland, Ohio. I think it is wonderful that you are fascinated with space, and it is great to hear you are considering a career in a space-related field.
There are many different types of engineers that work at NASA. A few of the many examples include: aerospace engineers (also called aeronautical and astronautical engineers), chemical engineers, materials engineers (like me), mechanical engineers, electrical engineers, polymers engineers, computer & software engineers, system engineers and planetary engineers. There are various specialized engineers also (such as optical engineers). Many of the NASA engineers have “desk” jobs where they work on computers for the majority of time. And other engineers, like me, spend part of the time in a laboratory doing experiments and research, and then part of the time at their desk doing computer work (analyzing & graphing data, writing reports and papers, etc). Some engineers may even work outside (truly “in the field”), for example doing weather testing or operating a test rover in desert-like terrain. I have experiments that fly on the exterior of the International Space Station to test the durability of spacecraft materials in the harsh space environment. And, of course, there are astronauts who get to work in space on the International Space Station!
So, in summary, there are many different things that NASA engineers may do. The best advice I can give is to pursue one of the engineering disciplines that sounds most interesting to you, and try to get a shadow opportunity or a summer internship at a NASA center to learn more from NASA engineers. You can also learn about women engineers and researchers at “Women @ NASA” (http://women.nasa.gov/). Good luck! Kim