I have a bachelor’s degree in aerospace engineering, and I heartily endorse everyone else’s recommendation of KERBAL SPACE PROGRAM. I’ve been playing KSP since March 2013 (!) and have thousands of hours in it. You will learn more basic orbital mechanics in the first few months of playing around with KSP than you would really learn in a similar time trying to understand the math from scratch, and you will get it intuitively far, far better. I spent an entire year of college in the dark ages of the late 80’s doing the math, plotting orbits on graph paper and writing simple time-step integrations in BASIC on an IBM PC to try to simulate a single simple propulsive maneuver semi-realistically. Today, KSP can SHOW you the same kind of maneuver as fast you can think it up, slap parts together and launch your rocket.
Just a wonderful not-so-little game that is far more than it seems to the uninitiated.