First of all cut out a small shape as shown from the cardboard.
Make two holes on both ends of it using any sharp object. Attach it to the chain using these holes as you see here.
Apply glue all over the piece. Stick the shells one by one to this cardboard piece. Let it dry well. Now it is the time to paint it.
Start from the bottom layer.
Here I am using different shades of pink. Apply purple shade on the bottom layer,
on top of that apply dark pink, then normal pink and finally very light pink.
Let it dry. See, we have made a beautiful pendant. It looks costly too, doesn't it?