In the mitosis of a cell, we can see the brilliance of nature at its highest. It seems like a very simple procedure, and it is very complicated in detail. It is to develop 2 diploid daughter cells from 1 diploid mother cell. Now, we'll try to explain mitosis in two ways: at a glance and in detail.
At a glance
This is what most people think what mitosis is, and it's really brief, but it'll give you an idea of what mitosis is (don't fix it in your mind. it isn't quite correct at some parts). When a cell is about to divide, it first duplicates its genetic materials, then the nucleus divides into two. After the nucleus divides, the cytoplasm constricts, and the cell membrane breaks into two, each include a complete set of chromosomes.
The real thing
Now, after looking at what most people think and having a rough idea of what mitosis is, we're ready to move to the real thing. Actually, mitosis consists of 6 different phases, naming Interphase, Prophase, Prometaphase, Metaphase, Anaphase and Telophase respectively. We'll now move to the details of each phase. What does the phase do, and what could we observe.
In the interphase, the DNA is spread throughout the whole nucleus, working on its day-by-day job: making proteins, and replicate themselves. In this stage, the DNA is not visible through light microscopes. When it finishes replicating, it moves on to the prophase.
In the prophase, the chromosomes begin to condense, and could now bee see in microscopes as "X" shape structures. The centre point of the "X" is called centromeres, and the two chromosomes on each side are called chromatids, each is actually a fully functional chromosome. It could now be safely hauled about. When the chromosomes condense, the cytoskeleton shifts and form 2 conical structures. This phase is the visible build-up of mitosis.
In this phase, the nucleus envelop breaks down (called nuclear envelope break down -- NEBD), letting the chromosomes out, floating in the cytoplasm.
This is probably the most brilliant phase of all. Here the centromeres of the chromosomes join the protein threads at where the cell is to divide. This is probably the straightest line one may see in nature.
The fibres contract. The centromeres are severed, and the two chromatics are yanked apart to the poles of the cones (remember the cones formed by the cytoskeletons?), each is now called a chromosome.
This is the phase where the cell restores order. The chromosomes now decondense, and the cytoplasm divides. The nuclear envelope is reformed after this.
Here ends the whole mitosis process. The cell then begin its daily work, and getting ready for another round of splitting.