var
  ExcelApp: OleVariant;
  anExcelFileName: String;
begin
  try
    ExcelApp := CreateOleObject('Excel.Application');
    anExcelFileName := 'D:sample.xlsx';

    ExcelApp.Workbooks.Open(anExcelFileName);
    ExcelApp.Visible := True;

    ExcelApp.Workbooks[1].Sheets[1].Range['A1'].Value := 'HELLO';
  except
    on E: Exception do
      showMessage('Error on something: ' + E.Message);
  end;
end;