The Arduino Nano is a small, complete, and breadboard-friendly board based on the ATmega328 (Arduino Nano 3.x). It has more or less the same functionality of the Arduino Duemilanove, but in a different package. It lacks only a DC power jack, and works with a Mini-B USB cable instead of a standard one.
You can buy this tiny little yet powerful board running on ATMega 238 chip from Amazon and moderate price and best reviews by clicking here.
You can download the datasheet of atmega 328 microcontroller from here.
Pin mapping of Arduino Nano board is shown below.
ARDUINO IDE (SOFTWARE)
For programming Arduino board, you required a software named Arduino. You can download this free software from Arduino’s website or you can just goto that page by clicking here.
GETTING STARTED WITH ARDUINO
Watch out this video and also watch out his episodes on Arduino to become expert in Arduino. Still if you have any doubt you can definitely ask me through mail email@example.com