Turning the wheel of the car, to turn the actual wheels, should be harder while a car is parked, than when a car is in motion.
BUT, what you are describing sounds like you are running low on steering fluid.
Go to auto zone, or walmart, or somewhere with car stuff (thats right.. i said car STUFF), and ask the dude behind the counter what type of steering fluid your car would take.
Then ask for a bottle.
Also, make sure you ask the guy at the auto parts store WHERE it goes.
I knew somebody that put steering fluid into his windshield wiper fluid box. Not good.