OK.. I built a colony ship and sent that with a few other ships to an open planet.. They arrived and I got a msg stating that the colonist were now developing the planet... My question is Now What??? What do I do next and what can I do with this colony?

Build mines to increase income of Your Empire.
Also you can develop sheeps ships production, Labs etc.

I recommend to read this litle, but useful manual Choice of planet before develop new Colonies.

Thanks Cap.. Good info..