At first controlling a 7 segment display seems quite complex but it quickly becomes clear.
What follows is a quick guide to control a 7 segment display with a arduino board
If you want to jump ahead to any other part here's your chance:
Step 1 - What Is A Seven Segment Display?
Step 2 - Parts & Tools
Step 3 - Testing
Step 4 - Built The Circuit
Step 5 - Project 1- One Digit Count Down Timer
Step 6 - Multiplexing
Step 7 - Project 2 - Two Digit Count Down Timer
This instructable is a entry in the arduino contest so if you like it please vote.
Step 1: What Is A Seven Segment Display?
Step 2: Parts & Tools
~ 2 x Seven Segment Display (Common Cathode)- Red,Blue
~ 1 x 330 ohm resistor - Sparkfun.com
~ Arduino Uno(Or equivalent) - Sparkfun.com
~ Breadboard - Sparkfun.com
~ Some jumper wires - Sparkfun.com
~ The arduino programming Environment - Arduino.cc
~ USB Cable A-B - Sparkfun.com
~ Soldering Iron - Sparkfun.com
~ Solder Wire - Leaded or Lead Free
The total cost should be about 8.10 $ assuming that you have a arduino,breadboard and all the tools