The nucleolus is located deeper into the center of the nucleus, the organelle that directs the cell. The nucleolus stores the cell's genes (DNA), proteins and creates ribosomes.
The gas tank in a car stores gas that can later be used for the car, like how a nucleolus stores RNA that can later be used to create ribosomes (fuel). Sadly, having a nucleolus inside of a nucleus isn't applicable for a car.