Power steering allows you to turn your car via the steering wheel without resistance. If you're having a hard time turning your steering wheel, chances are your power steering isn't working correctly. There are a few approaches you can take to determine what is causing your power steering to fail.
Check your power steering fluid. Locate the appropriate spot under your hood, using your car's manual if necessary. Refill if necessary. If it needed to be refilled, drive for a while and see if this fixes the problem.
Ensure none of the belts under your hood are broken or loose. A loose or broken belt can cause the power steering pump to stop turning. If the belt is loose or broken, take it to a mechanic shop if you don't have the expertise yourself to fix it.
If the fluid doesn't need replaced and the belts appear unbroken, the pump probably isn't working. Take your car into a mechanic shop. Explain you checked the fluid and belts. A certified mechanic will be able to determine whether your pump needs replacing.