The main workhorse is still the ATmega328P; however, the number of analog pins has gone up from four to eight. The other difference is the lack of a DC power connector. 

Learning Center:

Uploading Your First Sketch

1. Get the Arduino software if you have not already
   1. Download from http://arduino.cc/en/Main/Software
   2. Unzip the zip file to somewhere like C:\ (on Windows), so you will end up with a folder like C:\arduino-0022
2. Prepare for serial communication
   1. Connect the USB-B end of the cable into the board
   2. Connect the other end of the cable into a USB port on your PC/Mac
   3. If your computer prompts for drivers, point it to the “drivers\FTDI USB Drivers” subfolder of the Arduino software, e.g. “C:\arduino-0022\drivers\FTDI USB Drivers”
   4. You should now see the LED labeled ON near the reset button light up
3. Load the sketch
   1. Open the Arduino software
   2. Open the LED blink sketch: File menu > Examples > Basics > Blink
   3. Select the Arduino Nano: Tools > Board > Arduino Nano
   4. Select the serial port: Tools > Serial Port.  This is the serial port for the board’s built-in FTDI. If you do not know which one this is, you can find out by going into Device Manager > Ports (COM & LPT), and look for a “USB Serial Port (COMx)”
   5. Upload the sketch: File > Upload to I/O Board
   6. Wait for the “Done uploading” message in the bottom blue status bar
4. The LED labeled L near pin 13 should now blink slowly
5. Congratulations! You have successfully uploaded your first sketch to your board.