A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
I presume you are talking about workbook and worksheet templates. Then you need to put both Book.xltx and Sheet.xltx in XLSTART.
How to find XLSTART location -
C:\Users\User_Name\AppData\Roaming\Microsoft\Excel (replace user name with your user name, you can directly reach here by copy and pasting following without quotes in Explorer address bar - "%appdata%\Microsoft\Excel")
Note - If the above path is not applicable for your installation, you need to find XLSTART path. Excel folder contains XLSTART folder in itself (In case, your XLSTART path is not in Appdata)
Open Excel > ALT+F11 > If Immediate Window is not visible, type CTRL+G. Same can be also be accessed through View > Immediate Window > Type "? application.StartupPath" without quotes and press enter > You will have your path below.