Hier hast du ein einfaches Beispiel:
using Excel = Microsoft.Office.Interop.Excel;
var excelApp = new Excel.Application();
excelApp.Visible = true;
excelApp.Workbooks.Add();
Excel._Worksheet workSheet = (Excel.Worksheet)excelApp.ActiveSheet;
workSheet.Cells[1, "A"] = "ID Number";
workSheet.Cells[1, "B"] = "Current Balance";