All cells go through a cycle with four steps. G1, S, G2, mitosis, and cytokinesis. During the G phases, the cell grows, and during the S phase, all of the DNA is duplicated to prepare for the cell to divide. Vitosis is the act of the nucleus of a cell dividing. It has four stages and ends in the entire cell dividing and forming two new cells. It is the nucleus dividing, not the cell dividing. The first step of mitosis is prophase. During prophase, two key events occur. First the DNA condenses into chromosomes. For prophase, the DNA is unwound so that it can perform its function. Second, the nuclear envelope dissolves. This step is important to allow subsequent processes of mitosis to occur. The second step of mitosis is metapace. Vindal fibers attached to the centromere to the chromosomes, and start to pull on both sides. This forces the chromosomes to line up along the middle of the cell. Remember, the chromosomes are able to do this because the nuclear envelope dissolved during prophase. The third step of mitosis is anapace. During anapace, the spindle fibers pull the chromosomes apart. Duplicate copies of DNA were formed earlier, so each half of the chromosome is identical. The fourth and final step of mitosis is telophase. During telophase, the identical copies of each chromosome are pulled to the opposite poles of the cell. New nuclear envelopes begin to form around the chromosomes. After mitosis has occurred and two nuclei exist, the cell divides in a process called outside a chinesis, forming two new cells from one existing cell. Here you can see an actual cell going through all four stages of mitosis. Here's a slide of some onion cells. You can see that each cell is in a different stage from mitosis.