When you get a wound a scab forms and when it falls off you have new skin where before the wound was open. This occurs through the reproduction of skin cells. When the cells divide they create identical ‘daughter’ cells*. These ‘daughter’ cells are genetically identical to the ‘parent’.
In the nucleus of a cell there are chromosomes, which hold the DNA of that cell. When a cell splits so does the DNA, thereby creating an identical DNA, which is for the ‘daughter’ cell. The process of the cell splitting is called mitosis.
There are five main phases in mitosis. The first is the prophase in which the chromatids, a
chromosome almost fully split into two parts in the process of the DNA replication, get denser and denser in the nucleus of the cell. Next, in the metaphase, the chromatids line up in the middle of the cell, creating a line. In the anaphase, the chromatids fully separate (creating the two DNAs) and the chromosomes move to opposite ends of the cell. Two nuclei form and the cell begins it’s final stage in the telophase. Finally, in cytokinesis, mitosis is complete and the two cells separate.
This is how, through cell division, skin cells can cover up a wound.
*The term ‘daughter’ cell does not mean that the cell is female.