You can buy complete Arduino or you can have more fun and build one yourself.
What you will need:
4 x 100 nF capacitors
2 x 22 pF capacitors
1 x 10 uF electrolytic capacitor
1 x button
1 x 10K ohm resistor (brown, black, orange)
1 x 100 ohm resistor (brown, black, brown)
1 x 16MHz crystal
3 x breadboard male to male jumper wires
To program the Arduino you will need a UART (universal asynchronous receiver/transmitter) and five more jumper wires or an eight pin header. The UART usually comes with female to female wires and you need the header on the board to connect the UART wires. Alternatively, you can user the male to male jumper wires, which could be handy as it extends the cable for the UART slightly. Off course it does have the disadvantage that it gives an extra connection that could pull out but you can secure it with a bit of insulation tape.
When placing the ATMega controller, that is the big black chip in the middle of the board, make sure that you take note of its orientation. On the one side of the chip there is usually a half circult with a dot in line with what is pin one. You can see it on the diagram below.
You also have to make sure you place the electrolytic capacitor the right way round. On the diagram you’ll see a little white mark which indicates the negative side of the capacitor. The actual capacitor will also have a white or black line on one side, usually with minuses painted on the line. Usually the leg on the positive side is longer than the leg on the negative side. So you have two things to help you orientate the capacitor the right way.
The last component to check is the LED. The positive leg of the LED is the longer leg. If you have good eyesight you might also notice that on the positive side of the LED the little rim on the bottom is slightly flattened. On the diagram below, the longer leg has to be the positive leg.
Click on the image to get an enlarged view.