The SparkFun COM-08653 is a basic 12 button keypad for user input.

The buttons are setup in a matrix format. This allows a microcontroller to 'scan' the 7 output pins to see which of the 12 buttons is being pressed.

Check the examples below for correct pin-outs and such.

Datasheet COM-08653

PIC HEX Pad Tutorial

Notes from Arduino Instructable

Arduino Keypad Library

Alarm System Project from Lucid Science

Keypad Example from Bildr.org