If u haven't been trying for too long, then I'd recommend that you try tracking your cycle the natural way for now, to save obsessions and confusion. The average cycle length is 28 days (so day 1 is the day your period starts, day 28 is the day b4 your next period starts). But some girls have a shorter cycle, others longer. Basically, the best time for you to BD (do the baby dance - in other words, have sex) is just b4 u ovulate. Most women ovulate in the middle of their cycle (around 14 days b4 you period). But again, you may ovulate earlier, you may ovulate later. The way u can usually tell is thru your CM (discharge - ew!). When it gets clear and quite a lot of it, and stretchy (where it stretches quite a bit between your fingers) then that means you're fertile and this is the time to BD. You may also get little ovulating pains.
The best thing for you to do is BD every other day from the day your period stops though just to cover all bases. You could also keep a note somewhere of then your period starts and when you also think you ovulate each month.
If you want to be sure about when u ovulate, then do basal temping (as described by the lovely LoopyLew) or use ovulation predictor kits (OPKs) where you need to p on a stick from day 10 of your cycle and it'll tell you when you're about to ovulate. But these sometimes don't work.
Hope this helps and good luck! x
