LED (Light-emitting diode) has two pins. The positive end of a LED (larger pin) is called anode, and the negative end is called cathode.
This example shows the simplest thing you can do with an Arduino to see physical output: it blinks a LED!
In this tutorial you will also learn how to use pinMode() and digitalWrite() functions.
More info can be found here: http://www.ardumotive.com/how-to-blink-an-led-en.html
