Thanks

tell about the safe days to avoid pregnancy

Conception can happen at longest, 24 hours of the egg coming down, any longer than that and the egg will die. Implantation happens anywhere from 3 to 12 days. from your ovulation day
References :

Here is some better information that I hope answers your questions:

A woman’s monthly cycle is measured from the first day of her menstrual period until the first day of her next period. On average, a woman’s cycle normally is between 28-32 days, but some women may have much shorter cycles or much longer ones. Ovulation can be calculated by starting with the day the last menstrual period (LMP) starts or by calculating 12-16 days from the next expected period. Most women ovulate anywhere between Day 11 – Day 21 of their cycle, counting from the first day of the LMP. This is what many refer to as the “fertile time” of a woman’s cycle, because sexual intercourse during this time increases the chance of pregnancy. Ovulation can occur at various times during a cycle, and may occur on a different day each month.

The Ovulation Cycle Divided into Two Parts:
The first part of the ovulation cycle is called the follicular phase. This phase starts the first day of the last menstrual period (LMP) and continues until ovulation. This first half of the cycle can differ greatly for each woman lasting anywhere from 7 days until 40 days. The second half of the cycle is called the luteal phase and is from the day of ovulation until the next period begins. The luteal phase has a more precise timeline and usually is only 12-16 days from the day of ovulation. This ultimately means that the day of ovulation will determine how long your cycle is. This also means that outside factors like stress, illness, and disruption of normal routine can throw off your ovulation which then results in changing the time your period will come. So the old thought that stress can affect your period is only partly true. Stress can affect your ovulation which ultimately determines when your period will come, but stress around the time of an expected period will not make it late—it was already determined when it would come 12-16 days earlier!

From the Menstrual Period to Ovulation (the details you may not know!)
When your menstrual cycle begins, your estrogen levels are low. Your hypothalamus (which is in charge of maintaining your hormone levels) sends out a message to your pituitary gland which then sends out the follicle stimulating hormone (FSH). This FSH triggers a few of your follicles to develop into mature eggs. One of these will develop into the dominant follicle, which will release a mature egg and the others will disintegrate. As the follicles mature they send out another hormone, estrogen. The high levels of estrogen will tell the hypothalamus and pituitary gland that there is a mature egg.

A luteinizing hormone (LH) is then released, referred to as your LH surge. The LH surge causes the egg to burst through the ovary wall within 24-36 hours and begin its journey down the fallopian tube for fertilization. The follicle from which the egg was released is called the corpus luteum, and it will release progesterone that helps thicken and prepare the uterine lining for implantation. The corpus luteum will produce progesterone for about 12-16 days (the luteal phase of your cycle.) If an egg is fertilized, the corpus luteum will continue to produce progesterone for a developing pregnancy until the placenta takes over. You can begin looking for pregnancy symptoms as early as a week after fertilization. If fertilization does not occur the egg dissolves after 24 hours.

At this time your hormone levels will decrease and your uterine lining will begin to shed about 12-16 days from ovulation. This is menstruation (menstrual period) and brings us back to day 1 of your cycle. The journey then begins all over again.

References :
http://www.americanpregnancy.org/gettingpregnant/understandingovulation.html