HOW TO SELECT YOUR BABY’S SEX.
First of all Sperm cells are either X or Y. The Egg cell is always X. If X-Sperm cell meets the egg(X) the baby will be a Girl (XX). If Y-Sperm cell meets the egg(X), the baby will be a Boy (XY). The Y-Sperm cells move fast but die fast (its lifespan is about 24hrs). X-Sperm cells move slowly but survive longer (up to 3-4days).
Therefore you should know that is not too hard if you have intercourse some days before ovulation, most of the Y-Sperm cells would have died leaving mostly X-Sperm cells. The chances of having a Girl is therefore higher. To increase the CHANCE of conceiving with a baby Boy, intercourse must be timed to coincide with ovulation.
You can learn more about this at https://www.webmd.com/baby/features/choosing-sex-of-your-child