Thanks for your Query,
I think you are asking about safe sex
means safe for not being pregnant.during the period intercourse is the safest period.you gets no pregnancy
during that 4 days periods.
Usually in a regular cycle of 28 days ovulation takes place on 14th day so you should avoid sex during middle 10 days of cycle.as for example you have a period on 1st of july you should avoid doing sex from 10th of july to 20 th of july.
This method works only in 28 day's regular cycle.