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Ovulation occurs each month when an egg is released from one of the ovaries. Occasionally, more than one egg is released, usually within 24 hours of the first egg. At the same time, the lining of the womb begins to thicken and the mucus in the cervix becomes thinner so that sperm can swim through it more easily.  

The egg begins to travel slowly down the fallopian tube. If a man and a woman have recently had sex, the egg may be fertilised here by the man's sperm. The lining of the womb is now thick enough for the egg to be implanted in it after it's been fertilised.

If the egg is not fertilised, it passes out of the body during the woman's monthly period, along with the lining of the womb, which is also shed. The egg is so small that it can't be seen.

When is the fertile time?
Theoretically, there's only a short time when women can get pregnant, and that is the time around ovulation. It is difficult to pinpoint exactly when ovulation happens unless you are practising fertility awareness. In most women, ovulation usually happens around 10-16 days before the next period.

Fertility awareness can be used to plan or avoid pregnancy, but has to be taught by a trained fertility awareness instructor. It involves monitoring vaginal secretions, taking your temperature every day, and keeping a calendar of your cycle to help pinpoint when ovulation is likely to be happening. Maya has an ovulation tool you can use to find your fertile time of the month.

Vaginal secretions change during the menstrual cycle. Around the time of ovulation they become thinner and stretchy, a bit like raw egg white.
It is not accurate to say that women are fertile on day 14 of the menstrual cycle. This might be true for women who have a regular, 28-day cycle, but does not apply to women whose cycles are shorter or longer and irregular.