If your car is having trouble turning, especially when making sharp turns, it could be a sign that your differential fluid is low. Other signs include a burning smell coming from the differential area or gear changes that are not as smooth as they used to be.
If you think your differential fluid might be low, the best thing to do is to take it to a mechanic and have them check it. They will be able to tell for sure if the fluid is low and can top it off for you.