This page will get you started with tracking fertility signs -
http://www.medhelp.org/tags/health_page/133/Fertility/Ovulation-Tracker-Overview?hp_id=145.
From there, you'll know enough to find more resources if you're interested.
Best of luck! *sprinkles baby dust*
The old medical advice is that women ovulate on day 14 of their cycle, with the first day of one's period being day 1. So counting Dec 21 as the first day, the old advice would say you'll ovulate on Jan 3.
However, to truly know when you ovulate, you can buy an ovulation prediction kit or you can start to track fertility signs, such as your basal body temperature and cervical mucous. Or do both - track signs and buy ovulation prediction kits.
Lemme see if I can find information about tracking your fertility signs here on MedHelp.org.