Chromosomes are the variables whose values are adjusted in order to solve the problem.  Their value is related in some way to the fitness function.  The adjustable cells may be located automatically if you click on the AutoDetect button.  You may also type in the range of adjustable cells in the edit box, e.g., $C$4:$C$8 or use the mouse to highlight the cells in the spreadsheet.  Multiple ranges are allowed; simply separate the ranges with a comma, e.g., $C$4:$C$8, $I$15:$I$17.

Note: The AutoDetect button makes a guess based upon an examination of the formula in the fitness cell.  It detects all of the cells that are linked to the fitness function cell.  However, if your adjustable cells are only a subset of these, then you will need to delete all unnecessary cell references.