A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
When you double-click a .xls file in File Explorer, Excel opens that .xls file. If you then select File > Save or press Ctrl+S, Excel saves the changes to the existing .xls file.
When you double-click a .xlt file in File Explorer, Excel creates a new, unsaved workbook in memory that is a copy of the .xlt file. If you then select File > Save or press Ctrl+S, Excel displays the 'Save As' dialog, letting you save the workbook as a .xls file.
You can create a template if you frequently need to create a new workbook with the same design and/or formatting. Let's say, for example, that you need to produce a monthly report. The data will change from month to month, but the layout must be the same each time. You could save a workbook with the required layout as a template. Each month, you can double-click the template to create a new report.