A new file in Excel 2013 is called a workbook; the spreadsheet you work on is called a worksheet. By default, a workbook comes with one worksheet, although you can add more. The worksheets can be grouped together for simultaneous editing. After you make your edits, you can ungroup the worksheets to modify them individually.
Hold down the "Control" key while clicking specific worksheet tabs to group them. Spreadsheets that are linked together update at the same time. For example, if you group sheets 1 and 2 and type the word "test" in cell B2 on sheet 1, you can click over to sheet 2 and see the word "test" in the same cell. If you want to group multiple tabs in a row, select the tab for the first sheet you want to include in the group, hold the "Shift" key and click the last tab to group everything between the active tab and the one you click.
Ungrouping Excel Worksheets
When you're done with your edits, click a tab that isn't part of the group to disband the group. If every tab is linked, hold down the "Control" key and click any tab to deselect it from the group so it can be selected to ungroup the rest. Alternatively, right-click any grouped tab and select "Ungroup Sheets."