Controlling an LED
The hardware equivalent of hello world
is an LED flash, which is a great test to ensure that everything is working and that you have wired it correctly. To make it a little more interesting, I've suggested using an RGB LED (it has red, green, and blue LEDs combined into a single unit), but feel free to use separate LEDs if that is all you have available.
Getting ready
You will need the following equipment:
4 x DuPont female to male patch wires
Mini breadboard (170 tie points) or a larger one
RGB LED (common cathode)/3 standard LEDs (ideally red/green/blue)
Breadboarding wire (solid core)
3 x 470 ohm resistors
Each of the previous components should only cost a few dollars and can be reused for other projects afterwards. The breadboard is a particularly useful item that allows you to try out your own circuits without needing to solder them.

The diagrams of an RGB LED, standard LED, and RGB circuit
The following diagram shows the breadboard circuitry:

The wiring of an RGB LED/standard...