procedure TForm1.ExcelFileAddWorksheets(Sender: TObject);
var
   ExcelFileName: String;
   ExcelApplication, ExcelWorkbook, ExcelWorksheet: Variant;
begin
     //be sure ComObj and Variants units are included in the "uses" clause

     ExcelFileName := 'C:\PhysiologyWeb\delphi_code_examples\excel_file.xlsx'; //replace file name with the name of your file

     ExcelApplication := Null;
     ExcelWorkbook := Null;
     ExcelWorksheet := Null;

     try
        //create Excel OLE
        ExcelApplication := CreateOleObject('Excel.Application');
     except
           ExcelApplication := Null;
           //add error/exception handling code as desired
     end;

     If VarIsNull(ExcelApplication) = False then
        begin
             try
                ExcelApplication.Visible := True; //set to False if you do not want to see the activity in the background
                ExcelApplication.DisplayAlerts := False; //ensures message dialogs do not interrupt the flow of your automation process. May be helpful to set to True during testing and debugging.

                //Open Excel Workbook
                try
                   ExcelWorkbook := ExcelApplication.Workbooks.Open(ExcelFileName);
                   //reference
                   //https://docs.microsoft.com/en-us/office/vba/api/excel.workbooks.open
                except
                      ExcelWorkbook := Null;
                      //add error/exception handling code as desired
                end;

                If VarIsNull(ExcelWorkbook) = False then
                   begin
                        try
                           //Add a new worksheet. The new workshet becomes the first tab (from the left).
                           ExcelWorkbook.WorkSheets.Add(Null,Null,1,-4167);
                           //or
                           //ExcelWorkbook.WorkSheets.Add;
                           //reference
                           //https://docs.microsoft.com/en-us/office/vba/api/Excel.Worksheets.Add
                           ExcelWorkbook.Worksheets[1].Name := 'First Sheet'; //assumes any existing sheets do not have the same name

                           //add a new worksheet after the last existing worksheet in this workbook
                           ExcelWorkbook.WorkSheets.Add(Null,ExcelWorkbook.WorkSheets[ExcelWorkbook.Worksheets.Count],1,-4167);
                           ExcelWorkbook.Worksheets[ExcelWorkbook.Worksheets.Count].Name := 'Last Sheet'; //assumes any existing sheets do not have the same name

                           //connect to Excel Worksheet using either the ExcelApplication or ExcelWorkbook handle
                           ExcelWorksheet := ExcelWorkbook.WorkSheets[ExcelWorkbook.Worksheets.Count]; //gets the last worksheet in this workbook
                           //reference
                           //https://docs.microsoft.com/en-us/office/vba/api/Excel.Worksheets.Item
                        except
                              ExcelWorksheet := Null;
                              //add error/exception handling code as desired
                        end;

                        If VarIsNull(ExcelWorksheet) = False then
                           begin
                                ExcelWorksheet.Select;
                                ExcelWorksheet.Cells[1,1] := 'We created this worksheet as the last tab.'; //[row,column], in this case, text is added to Cell A1
                                ExcelWorksheet.Cells[2,1].Select; //selects Cell A2
                           end;

                        ExcelWorksheet := Null;
                        try
                           ExcelWorksheet := ExcelWorkbook.WorkSheets[1]; //[1] specifies the first worksheet
                        except
                              ExcelWorksheet := Null;
                              //add error/exception handling code as desired
                        end;

                        If VarIsNull(ExcelWorksheet) = False then
                           begin
                                ExcelWorksheet.Select;
                                ExcelWorksheet.Cells[1,1] := 'We created this worksheet as the first tab.'; //[row,column], in this case, text is added to Cell A1
                                ExcelWorksheet.Cells[2,1].Select; //selects Cell A2
                           end;

                        //now save the file
                        ExcelWorkbook.SaveAs(ExcelFileName);
                        //or
                        //ExcelApplication.WorkBooks[1].SaveAs(NewExcelFileName);
                        //Note: The file is saved using the same name. Therefore, the modified file overwrites the original one. Simply change the file name parameter to save using a different file name.
                        //reference
                        //https://docs.microsoft.com/en-us/office/vba/api/excel.workbook.saveas
                   end;
             finally
                    ExcelApplication.Workbooks.Close;
                    ExcelApplication.DisplayAlerts := True;
                    ExcelApplication.Quit;

                    ExcelWorksheet := Unassigned;
                    ExcelWorkbook := Unassigned;
                    ExcelApplication := Unassigned;
             end;
        end;
end;