It can be due to many different reasons, first check your coolant level, second look for leaks or damaged hoses, if everything checks ok you may have to have it inspected by a professional, it can be anywhere from thermostat, water pump bad cap and all the way to a bad head gasket, just to rule out the fan, turn on AC and check if the cooling fan infront of the motor kicks in. If coolant level and fan not working are not the reason for the car to overheat, it is recommended that you have your car towed to a repair shop or you may cause permanent damage to the motor.