Everyday, our organism has to renew cells. Indeed, some die and some must be created. During the growth, we need more cells with the same DNA.

The process to produce DNA and to prepare cell division is called mitosis.

Video showing the stages of cell cycle:

https://www.britannica.com/video/73105/cell-cycle-events-division-process

To learn more : https://www.ck12.org/book/ck-12-biology-concepts/section/2.35/