Explain the rhythm method in sex?

Explain the rhythm method in sex?
It was promoted as a natural, safe method of Contraception, largely amongst the Catholic groups.
This is a form of contraception that relies on abstinence (no sex) during a woman's fertile period - 4 days prior to ovulation, the day of and the day after. At first it was done just using timing - charting your periods - relying on the fact you ovulate 14 days before the first day of your next period, which isn't very reliable as even a woman who's cycle is usually regular can have the occasional odd cycle.
Then the advanced method "Billings Method" became more common, where there were other signs of ovulation taken into account. The mucus discharge starting 3 days before ovulation, thickening until ovulation, then disappearing the day after. The slight rise in internal temperature on the day of ovulation (taken in the vagina in the mornings). And some even use the Ovulation Hormone tests available at the shops.
Strangely enough this knowledge also lets a couple plan for a pregnancy as well, giving a clear indication of when, and whether or not, a woman ovulates.
if you dont know about having sex,then you must be too young.this question,you should be asking your parents,not us.