i am telling you its damn easy and will take only about 30 mins max if you have everything you will need in hand !!
Things You Will Need :
1) 7 Segment LED (8 if you include the dot)
2) 5 Pin connector
3) 3V Coin cell
4) Coin Battery Holder
5) Hot Glue Gun or solder iron (glue gun would be much easier)
6) Double side tape
7) A ring (preferably flat - cylindrical)
Step 1: Basic introduction to 7 segment LED
See the pic below
> Every Red line indicated that its positive.
> Green lines indicated its the Ground or Negative.
> Each Pin Corresponds to a particular LED on the 7 segment.
> a,b,c,d,e,f,g as marked in the diagram below.
There are 2 types of 7 segment leds .. Anodic and Cathodic..
No issues seriously.. its just the polarity difference..
In the other type.. all reds will have to be ground and green will be positive.
Connect the green to ground. Then to which ever pin you give a positive supply of 3V that corresponding LED will glow !