quincy... I graduated with a Business degree and work in the corporate world, yet I have learned to build a robot...
The three main diciplines are mechanical engineering, electical engineering, and programming.
For someone like myself, I am pretty handy and and mechanically oriented, so although I can't engineer bipedial walking gates (for example), I can figure out how how to mount a motor on a frame and compute how fast my robot will travel if I know the speed of my motor and the circumference of the wheels.
I stuck a few paper clips in an electrical outlet and learned the difference between volts, amps, and resistance pretty quickly (no, just kidding), but there are a million "tutorials" on electronics that one can find on the web (which I continue to find and study!)
I took a BASIC programming class in high school over 25 years ago, so although I still think that "java" is a cup of coffee, I can program Parallax Stamps and PICAXE micro controllers.