There can be multiple sheets. At the bottom of the screen are small tabs that may say 'Sheet1', 'Sheet2', 'Sheet3', and so on. All of these sheets are said to comprise a 'Workbook'.
When you save your worksheet, the program will actually automatically save all of the sheets (i.e., the whole workbook) for you. However, when printing, in order not to waste paper, you will be given the choice of whether you want to print the selected displayed sheet, or the entire workbook (i.e., all of the sheets).