Cells go through a repeating series of events called the cell cycle. It ends with the cell dividing into two. Most of the cycle is spent in interphase. During interphase the cell grows, makes new organelles such as mitochondria and ribosomes, and copies its DNA so that each chromosome is doubled.
The cell then divides by mitosis, which has four stages. In prophase the chromosomes become visible and the nuclear membrane breaks down. In metaphase the chromosomes line up across the middle of the cell. In anaphase the two copies of each chromosome are pulled apart to opposite ends of the cell. In telophase a new nuclear membrane forms around each set of chromosomes.
Finally, in cytokinesis the cytoplasm and cell membrane divide, and two new cells are formed. The cycle can then start again in each new cell.
