Human fertilisation is the union of a human egg and sperm, usually occurring in the ampulla of the uterine tube. It is also the initiation of prenatal development. (from Wikipedia)
Once your egg has been released and your partner has ejaculated sperm into your vagina, fertilisation can occur anytime thereafter in the fallopian tube.
When ejaculation occurs, some of the sperm will leak out of your vagina again.
Some sperm will find their way and begin to swim up through your cervix.
At the time of ovulation the mucus in the cervix is thinner than usual to let the sperm pass through more easily.
The sperm swim into the womb and so into the Fallopian Tube
(The womb or uterus is where your baby grows. The size of the womb increases as your baby as your baby grows. A few weeks after birth of your baby, the womb contracts to its original size (about the size and shape of an upside down pear). The Fallopian tube is the tube that connects the ovary and the uterus. This is the place where fertilisation takes place between egg and the sperm if you have intercourse around the time of ovulation.
One sperm may then join with the egg and fertilise it. Conception is said to have taken place. (If anything was to happen, this was the time!)