Skin repairs itself by allowing the cells in the stratum basal to divide and heal. The skin is a highly regenerative tissue.
The epidermis is the outermost layer of the skin. For most small cuts, this is the only layer of the skin that will be affected. The stratum basale is the part of the epidermis that allows for regeneration by dividing the cells and repairing the epidermis layer. However, deeper cuts require that the stratum basale first be replaced and then the stratum basale can begin the process of regeneration by dividing cells.
Doctors give stitches to patients with particularly deep cuts because with stitches the stratum basale does not have to worry about growing too much laterally. Instead, it can focus on re growing in other directions leading to a much faster healing process.
With some cuts and burns, the injury is too deep and it enters the dermis. When it enters the dermis it leads to bleeding. The blood that begins to flow outside of the patient's blood vessel will then begin to clot and form a scab. The scab is created to help prevent any further blood loss and to keep infections from getting inside. As the cells work to divide and regenerate, the clot will be removed as well as the scab material by macrophages.