What is this component called and how can I use it in a sketch?

I've made a small album here. http://imgur.com/a/TuvYe

It came in a kit I ordered from but I'm not able to discern what it does or how to use it in a sketch. I'd be really grateful for your thoughts.

Thanks.

That's a potentiometer:

http://en.wikipedia.org/wiki/Potentiometer

The "103" on top marks it as a 10k (10 kilo-ohms) potentiometer. You can use it to set a variable voltage into the Arduino, and use that voltage to control something else that's variable (speed of a motor, brightness of an LED, etc.)

Have a look at the AnalogInOutSerial sample sketch in the Arduino GUI (File->Examples->Analog->AnalogInOutSerial)

-- The Flexible MIDI Shield: MIDI IN/OUT, stacking headers, your choice of I/O pins

@RuggedCircuits: Thanks for the help, that clears things up quite a bit.

More precisely its a "preset potentiometer" - designed to be on a circuit board to be adjusted once or twice when the circuit is commissioned. Typically it would be used to set an exact frequency / voltage /current level to compensate for component variability in the rest of the circuit. It won't survive heavy use for which a panel-mounted potentiometer is the device of choice