You have a single cell. Then the chromosomes line up along the axis of the cell with the centrosomes at the two poles of the cell. Then the chromosomes duplicate and form a pair of reduplicated chromosomes, two chromosomes identical to each other, connected in the middle by a centromere. It would be more logical for them to be called "duplicated" but the word is "reduplicated". The chromosomes on one side are connected by spindle fibers to the centrosome on that side, and the chromosomes on the other side are connected by spindle fibers to the centrosome on that side. Then the centromeres break, and the spindle fibers contract. The chromosomes on one side go to one side of the cell, and the chromosomes on the other side go to the other side of the cell. Then the opposite cell walls get closer and it divides into two cells. This is mitosis.
In meiosis, not the chromosomes but pairs of chromosomes line up along the axis of the cell. They duplicate. Each pair of reduplicated chromosomes is connected to the nearest centrosome by a spindle fiber. The spindle fibers contract, and half the pairs of reduplicated chromosomes go to one side of the cell, and the other half go to the other side. The cell divides in half. Within each of the two new cells, the pairs of reduplicated chromosomes line up along the axis, and each chromosome is connected to the nearest centrosome by a spindle fiber. The centromeres break, the spindle fibers contract, and the chromosomes go to the appropriate side of the cell. Each cell divides in half, leaving four cells, each with half the number of chromosomes as the original cell. These cells with haploid chromosomes are called gametes.
