1. Fertilization: It all starts with a sperm meeting an egg. This usually occurs in the fallopian tube. The sperm fertilizes the egg, creating a single fertilized cell called a zygote.

2. Cell Division: The zygote undergoes rapid cell division, multiplying as it travels down the fallopian tube towards the uterus. This dividing mass of cells is called a morula.

3. Blastocyst Formation: As cell division continues, the morula transforms into a hollow sphere called a blastocyst. The blastocyst has an outer layer of cells (trophoblast) and an inner cell mass.

4. Implantation: Around day 5 or 6 after fertilization, the blastocyst reaches the uterus and implants into the uterine lining (endometrium). This is a critical stage for embryo development.

5. Development of Layers and Placenta: The trophoblast layer of the blastocyst develops into the placenta, a vital organ that nourishes the embryo and removes waste products. The inner cell mass differentiates into three germ layers:

Ectoderm: This layer gives rise to the skin, hair, nails, and nervous system.
Mesoderm: This layer forms muscles, bones, connective tissues, the circulatory system, and the urogenital system.
Endoderm: This layer develops into the lining of the digestive tract, respiratory system, and some internal organs.

6. Organogenesis: From these three germ layers, all the organs and body structures of the embryo begin to form in a specific order and location during organogenesis.

7. The Embryo to Fetus: By the end of the 8th week, the embryo has developed most of its major organs and is now referred to as a fetus. The fetus will continue to grow and mature in the uterus throughout the rest of the pregnancy.