Specialized Cells & Differentiation

 Every 'complex' organism, is built out of cells, and these cells are known as specialized cells.
For humans, those would be and there are over 200 times of specialized cells in humans, muscle cells, nerve cells, and sperm cells. While a plant will have Root cells, Phyleom cells, and Xylem cells.

Let's take a Sperm cell, they take generic material to an egg cell, and sperm cells have half the genetic material to make an adult cell.
Because it is meant to combine with the egg cell to make one adult cell, they have a tail named the Flagellum and mitochondria to help the sperm swim through the uterus and the fallopian tubes to reach the egg cell and at the tip is a digestive enzyme to break a hole in the egg. 

Nerve cells and Red blood cells are completely different due to differentiation, as they are used in the body for completely different reasons.

Zygotes are fertilized egg cells, which will duplicate due to mitosis  and then they can differentiate into other cells, like red blood cells, nerve, muscle or skin cells.