I think you need to read the chapter in your course text book. If you had a lecture on s*x nd fallen asleep during it, I dont think I can help
Either the answer is anatomical, with the sperm travelling through the cx, uterus, fallopian tube
or else it is histological
When the sperm fertilises the egg, there is a charge density change which prevents other sprem fertilising the egg. The ovum completes meiosis and the second pro-nucleus is extruded. The sperm head joins the ovum nucleus and this makes up the complement of chromosomes. A little later in mammals, the nucleus and cytoplasm undergo unequal division into two
etc etc
I mean honestly this is in a million text books and hasnt changed for 150 years.