Taken from turnfast.com
Loose handling-- (a.k.a. oversteer) occurs during cornering when the car's rear tires lose traction before the front tires. When this happens, the car begins to rotate about its center of gravity, and the back of the car swings out from the intended driving line.
Understeer-- (a.k.a. push, tight handling) occurs during cornering when the car's front tires lose traction before the rear tires. When this happens, the car will not turn as much as intended by the driver's steering input, and will start to drift to the outside of edge the turn.
Check out "weight transfer" and "anti-roll bars" in the "handling" section of
Turnfast.com
Actually read everything you can find on that site, it rocks...has helped me a ton. But just read those two to answer your question.