Starts with one human cell containing 46 chromosomes
Ends up with
2 cells each containing 46 chromosomes
When growth or replacement cells are required for the body, mitosis occurs. The chromosomes copy themselves and then attach themselves to the original.
All these chromosomes then line themselves up and split down the middle to form a duplicate of each other as the cell divides.
Simplified, mitosis in a nucleus with just four chromosomes would be as follows:
Mitosis produces two identical cells.