The sperm enters through the vagina. The vagina has deadly acids meant to kill any invading bacteria or substances. Within the first 30 minutes, abnout 99% of the sperm is dead.
The surviving sperm enter the cervix. Usually blocked by mucus, the entrance of the cervix is cleared so the sperm can travel through. Due to the many passageways in the Cervix, most of the remaining sperm dies due to getting lost or stuck in the passageways.
About 3,000 sperm remain. Contractions help propel the sperm towards the Fallopian Tubes. White Blood Cells attack the sperm. The surviving sperm must search for the small doorway to the Fallopian tube.
The few remaining sperm enter the Fallopian Tube. Here they are safe from the white blood cells and can receive nutrients from the Fallopian Tube, allowing them to live longer.
The last few sperm need to find the egg. The egg is released. The sperm shed layers of protein so they can find the egg and fertilize it (capacitation). The sperm that makes contact with the outer coat of the enzyme has a bag of enzymes on its head which will enter the egg.
The zygote (egg and sperm) travels down the fallopian tube, going through cell division. The embryo breaks out of the protective layer and implants into the wall of the uterus to begin growing.