Here's a breakdown:

* Fertilization: A sperm cell fertilizes an egg cell. This union creates a single cell called a zygote.

* Cleavage: The zygote undergoes rapid cell division, forming a ball of cells called a morula.

* Blastulation: The morula develops into a blastocyst, a hollow ball of cells with an inner cell mass.

* Implantation: The blastocyst implants into the uterine lining.

* Gastrulation: The inner cell mass of the blastocyst reorganizes into three germ layers (ectoderm, mesoderm, and endoderm), which will give rise to all the tissues and organs of the body.

So, in essence, the embryo develops from the single-celled zygote through a series of developmental stages.