Assuming there is only one word in each cell in the column, the following
macro will put a comma after each word in the column containing the cursor.
Empty cells are ignored
Dim oCell As Cell
With Selection.Columns(1)
For Each oCell In .Cells
If Len(oCell.Range) > 2 Then
oCell.Range.InsertAfter Chr(44)
End If
Next oCell
End With