Nano V3.0 ATmega328P ( Arduino Compatible ) Micro-controller Module with USB Mini-B connection and CH340G USB to serial chip on board.

The Arduino Nano can be powered via the Mini-B USB connection,  6-20V unregulated external power supply (pin 30), or 5V regulated external power  supply (pin 27). The power source is automatically selected to the highest  voltage source.

The CH340G chip on the Nano is only powered if the board is being powered  over USB. As a result, when running on external (non-USB) power, the 3.3V output  (which is supplied by the CH340 chip) is not available and the RX and TX LEDs  will flicker if digital pins 0 or 1 are high.
Input and Output

Each of the 14 digital pins on the Nano can be used as an input or output, using  pinMode(), digitalWrite(), and digitalRead() functions. They operate at 5 volts.  Each pin can provide or receive a maximum of 40 mA and has an internal pull-up  resistor (disconnected by default) of 20-50 kOhms. In addition, some pins have  specialized functions:

Serial: 0 (RX) and 1 (TX). Used to receive (RX) and transmit (TX) TTL serial  data. These pins are connected to the corresponding pins of the CH340G USB-to-TTL  Serial chip.

External Interrupts: 2 and 3. These pins can be configured to trigger an  interrupt on a low value, a rising or falling edge, or a change in value. See  the attachInterrupt() function for details.

PWM: 3, 5, 6, 9, 10, and 11. Provide 8-bit PWM output with the analogWrite()  function.

SPI: 10 (SS), 11 (MOSI), 12 (MISO), 13 (SCK). These pins support SPI  communication, which, although provided by the underlying hardware, is not  currently included in the duino language.

LED: 13. There is a built-in LED connected to digital pin 13. When the pin is  HIGH value, the LED is on, when the pin is LOW, it's off.

The Nano has 8 analog inputs, each of which provide 10 bits  of resolution (i.e. 1024 different values). By default they measure from ground  to 5 volts, though is it possible to change the upper end of their range using  the analogReference() function. Additionally, some pins have specialized  functionality:

I2C: 4 (SDA) and 5 (SCL). Support I2C (TWI) communication using the Wire library  (documentation on the Wiring website).

There are a couple of other pins on the board:

AREF. Reference voltage for the analog inputs. Used with analogReference().

Reset. Bring this line LOW to reset the microcontroller. Typically used to add a  reset button to shields which block the one on the board.