Download the template, but don't open it directly — if you already have, close it without editing.
Open a new Excel sheet, then select "Get Data from Text" from the menu (or "Get External Data" if that option isn't shown).
In the window that opens, select the downloaded template and click "Import."
Configure the import: choose "Delimited" under "Original data type" and click "Next"; set the delimiter to "Comma" and click "Next"; select all columns, set "Column data format" to "Text," then click "Finish."
In the "Import Data" window, confirm "Existing worksheet" ($A$1) is selected, then click "OK."
Enter your data — see the "About Importing" article for details.
Save as CSV: go to File → Save As, choose a location, then select "CSV (Comma delimited)" as the file type.
To check the saved data afterward, reopen the file using steps 1–6.