To edit an existing workbook, tap on the workbook in the file list. The workbook will then open into the workbook window, ready for you to edit.
If the iPad is landscape orientated, the file list will appear to the left of the workbook window. If the iPad is portrait orientated, you can show the file list by pressing the Open button at the top left of the display. If another workbook is already open, you must first close it by pressing the Close button. When the workbook is closed, this button will change to an Open button, allowing you to select a new file to open.
Once you have opened a workbook, you can show or hide the keyboard by pressing the keyboard button at the top right of the workbook window.