To create a new workbook, tap the (+) button in the top right corner of the files folder window.
You will then be asked to enter a name for the new workbook.
You don't need to add a file extension. Sheet2 HD will do this for you automatically. Just enter a name. You can choose to show or hide file extensions from within the settings. A blank workbook will open. To start editing the spreadsheet, select the cell you wish to change and press the keyboard button at the top right of the screen.