Assembly: Microsoft.Office.Interop.Excel (in microsoft.office.interop.excel.dll)
Use the Worksheets property to return the Worksheets collection.
Use the Add method to create a new worksheet and add it to the collection.
Use Worksheets(index), where index is the worksheet index number or name, to return a single Worksheet object.
The Worksheet object is also a member of the Sheets collection. The Sheets collection contains all the sheets in the workbook (both chart sheets and worksheets).