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You can turn any of your worksheets into templates by selecting the "Excel Template (*.xltx)" format when you save the file. This will save the current spreadsheet into your Templates directory. You can also download a variety of templates from Microsoft when creating a new file. When you insert a template as a sheet, it will be added in front of the tab you have selected. This will open a new window allowing you to select what you want to insert. Your downloaded and saved templates will be listed in the "General" tab. Select the template you want to use and click "OK." Your new tab (or tabs if the template had more than one sheet) will be inserted in front of the tab you had selected.

Summary:
Create or download the template you want to use. Right-click the tab you want to insert the template in front of. Select "Insert" from the right-click menu. Select the template you want to insert. Select your new tab.