The father, son, and holy spirit are a triad.  Chapter three is about another special trinity: endo,  ecto-, and meso-derm.  This picture, from this site, shows the single layer of cells in a blastula becomes the three germ cells from which all other cells that you are made from will develop. 

Looks bit complicated, but this is much simpler than what happens next.  From each of these three layers, the different organs will develop:

• skin and brain from ectoderm cells;
• gut and digestive organs from endoderm cells; and
• bone, muscle, and circulatory system from mesoderm cells.

These are just some  examples of the ~200 different types of cells that make up your body.  Organs are collections of the same types of cells; each provide a uniques set of functions for life.  Like the heart pumping oxygen and nutrients to all the cells of your body, and taking away the by-products of their molecular machinery of life, or biochemistry.

But let’s go back to your story.  Created when an egg and sperm became one,  a zygote (single cell) is when you start, your moment of creation.  Soon after a day has passed, one cell has become two.  The next divisions are faster and create  4,  8, 16 and 32 cells; making a solid ball of cells, a morula (Latin for mulberry).

As the 32 cells become 64, then 128 the solid, uniform ball of morula becomes blastula. At one end a gap is created,  The dividing cells grow into this gap, and in a process called gastrulation where the three germ layers emerge.  Each layer of cells with distinct characteristics driven by their position inside, outside or in the middle.

The endoderm, ectoderm, and mesoderm mean skin that is inside, outside, and in the middle, respectively.  These three germ cells layers are created by an infolding (gastrulation)  from the single layer of cells in the blastula.  I find it hard to imagine, even with the help of the picture here.  But may be you will be able to.  If you physically try it with a flexible ball, you may get a better idea of how it works.

The total size of morula is about the same size as zygote; the dividing cells are able to obtain some nutrients in the womb. Sometime in the second week of your life, when you are somewhere between blastula and gastrula, you  implant into the cells of the womb, waiting to welcome you.  The interaction between embryonic cells and maternal cells will create the placenta and umbilical cord that will feed you and give you oxygen until you are born.

Your story, starts with one cell.  By the time you are born, you cells now number in the trillions (10^12 or 1 with 12 zeroes). Once born into the world, you are now exposed to the  risk of  bugs: microbial infections: bacteria, viruses and other parasites. You are born with natural defences against these, and also an immune system  that can be ‘trained’ to protect against specific bugs.  But that’s for another day.

Fun fact:  The egg that became you was created when your mother was still in her mother’s womb.  So, you started life in your gran’s tummy, not your mum’s.  Sperm are created daily.  Our creation, as the products of our parents connects us to the past; through our parents, then their parents, and so on.  To the dawn of time…

Odd arithmetic: 1+1= 3:  (1) Mum + (1) Dad  become a family of three, when you are born. And more as the family grows. In the case of sperm and egg,  1 + 1  = 1 zygote. And the strange story of matter and anti-matter that together become nothing (1+1=0).  Strangely, this means that from nothing we can get something in the reverse process that is constantly happening in the sub-atomic world of this strange  quantum physics…