Clarissa,
VFP doesn't natively, even in VFP8, support cell-by-cell highlighting like a spreadsheet. I don't know if any of the grid classes in the libraries here support it or not.
You might check some of the activex grids too, the MSFlexgrid may support this feature.
>I don't know how to enable user to use his/her mouse to highlight cells within a column or a row of a grid. And how do we know which cells have been highlighted?