There are two kinds of cell division: mitosis and meiosis. Mitosis is essentially a duplication process: It produces two genetically identical "daughter" cells from a single "parent" cell. You grew from a single embryonic cell to the person you are now through mitosis. Even after you are grown, mitosis replaces cells lost through everyday wear and tear. The constant replenishment of your skin cells, for example, occurs through mitosis. Mitosis takes place in cells in all parts of your body, keeping your tissues and organs in good working order.
Meiosis, on the other hand, is quite different. It shuffles the genetic deck, generating daughter cells that are distinct from one another and from the original parent cell. Although virtually all of your cells can undergo mitosis, only a few special cells are capable of meiosis: those that will become eggs in females and sperm in males. So, basically, mitosis is for growth and maintenance, while meiosis is for sexual reproduction.