In the simplest of terms, a Homo sapien is just a big bag of salt water with a whole bunch of chemicals thrown in the mix. It so happens that these chemicals are needed to be arranged in certain ways so that the bag of salt has organization and function. The control panel to all this organization lives in the center of the big house called a cell. The room that it lives is called a nucleus, and from this room the control panel directs the rest of the house. It is from this nucleus that orders are given to the cell (the rest of the house) on what it is to do, how it is to do it, and what it needs to carrying all this out. These directions are placed in special containers called a double helix and stored in boxes called a chromosomes.
The chromosomes are first brought together by specialized cells called gametocytes (more commonly called sperm and ova which only contain one half of the control panel). On first contact (union) they duplicate their own control panel and 23 maternal and 23 paternal chromosomes split into two halves. This splitting allows for the restoration of the full number of chromosomes (46) and decides the sex of the new Homo sapien. At random, this union joins the chemical materials that carry the speical messages known as DNA into a new person. What mystery it is.