Spermatogenesis is the process through which immature sperm cells called spermatogonial stem cells (which are actually stem cells) are transformed through a series of different types of cell divisions to produce mature sperm cells called Spermatozoa.
Spermatogonia (or Spermatogonium singular) are undifferentiated spermatogenic cells that need to be differentiated through the processes of mitosis and meiosis before they become mature sperm cells.
Spermatogenesis occurs in the seminiferous tubules of the testis. Both Spermatogenesis and Oogenesis are forms of Gametogenesis (formation of male and female gametes from primordial germ cells).
Testicles are constantly producing new sperm in spermatogenesis. The full process takes about 64 days. During spermatogenesis, testicles make several million sperm per day — about 1,500 per second. By the end of a full sperm production cycle, you can regenerate up to 8 billion sperm.
The main difference between spermatogenesis and spermiogenesis is that spermatogenesis is the formation of sperm cells whereas spermiogenesis is the maturation of the spermatids into sperm cells. Spermatogenesis is the complete process of the production of the sperm cells from the cells of the germinal epithelium of males. On the other hand, Spermiogenesis is the final differentiation and maturation process of the spermatids into sperm cells.