This is a power amp board for small audio amps (or anything else that needs 12V DC). It takes the output of a small transformer and rectifies it to DC. I use it with a small 120/12 1.5A Radio Shack transformer. It is designed to use the following parts (or something similar):

Bridge Rectifier (Mouser: 750-DF204-G)
LM7812 Voltage Regulator (TO-220 package)
D1 1N4001 Rectifier Diode

C1 2200µF 25V electrolytic capacitor (667-EEU-FR1E222S)
C2 0.1 µF film capacitor (647-QYS1H104JTP) - (or any similar cap with 5.08mm lead spacing)
C3 220 µF 25V Electrolytic (667-EEU-FM1E221)

R1 1.5k Ω 1⁄4W metal film resistor (lower value = more bright; higher value = less bright)
LED 3mm (whatever color you like)

Note: The hole in the board is sized for a small #4/40 bolt to attach it to a chassis with a spacer.