Download Arduino Nano Pin Diagram Gallery. They use the same processor (atmega328p) and hence they both can share the same program. The arduino nano pins, similar to the uno, is divided into digital pins, analog pins and power pins.
Arduino nano has similar functionalities as arduino duemilanove but with a different package. The board has 14 digital pins that can be used as input/output. The 5v pin of the arduino nano is directly connected to the 5v voltage regulator and supports a maximum current that is defined by the difference of the current provided by the voltage regulator and the current from the atmega328p.
These secondary pins are mostly communications pins such as i2c and spi.
I found that pinout diagram for arduino nano contains an error, in right side: I was looking for a cheapest possible option to get arduino and wireless comms for a dimmable light and come across this ebay item when searching for arduino nano clone. There are pins with secondary functions on the table below. Aref stands for analogue reference.