For anyone who doesn't understand what "control" is, the following is a small example of the work of a "control engineer". In this case, the engineer is one of my students. He's an undergraduate in a class I taught last quarter; this YouTube video is a demonstration of his final project for the class:As shown, his controller manages to keep the helicopter stabilized in a position that gets set by the joystick. The computer "flies" the helicopter with a heading set by a human via joystick. When they push on the helicopter, they're simulating a disturbance like a heavy wind gust. The helicopter's controller quickly brings it back to its old state. What you don't see is that the controller has been designed to do this as smoothly as possible (e.g., to prevent "jerkiness" within the helicopter).
This is a concrete example of classical control design. What I do in particular in my own research is quite a bit different. However, the video is a nice demonstration about what "control engineers" (like me) do.