>New to VFP.
>How can I execute an edit form from a cell/row in a grid?.
>How can I in return have the edit form update the cell/row in the grid, after I have closed the edit form.
>
>Note: The original form has a list box as a parent to the grid.

Normally you could bind edit form to some event of column.control (cell). I think RightClick event is a nice place. If you want to activate editform by row, you should consider AfterRowColumnChange event with ActiveRow property.
Returning from edit form you should Refresh grid (RecordSource supposedly changed in the form).