Let's see if we can visualize this process. A tiger ovum (egg) is fertilized by a tiger sperm. This process of fertilization results in a fertilized egg called a zygote. Initially, the zygote is only one cell. But then that one cell divides into two, thanks to a process called mitosis. The two cells then divide into four, the four into eight...you get the picture.
Eventually, the ball of cells is big enough to be called an embryo. It has the developments of major organ systems, such as the circulatory and nervous systems. This is a big time development! Much more than that single cell we had to begin with, the zygote.
A little more time passes by. The cells continue to divide, the systems continue to develop. The tiger embryo now actually is starting to take on the outward resemblance of a tiger cub, with physical features clearly present, such as eyes, nose, all four paws, and even a tail. The embryo is now developed enough to be called a fetus.
At full term, the cub is born. It will nurse on it's mother's milk and continue the process of cell division, gaining more body mass and control over that body as each day passes. As the cub matures into a young tiger, the endocrine system uses a set of hormones to give it female tiger characteristics, or male characteristics, if it is a male.
When you look back down the road, from where you came from, an old Chinese proverb has much meaning: "A journey of 1000 miles begins with a single step."