This article provides an overview of steps
Please be aware: The functionality of saving a site as a template described in this article is supported in SharePoint Online (classic sites only). More information read in Microsoft documentation
How to create a site template
1.To create a template, you need to go to the course that you want to use as a template -> gear icon -> Site Contents - > Site Settings -> Site actions block -> Save site as a template.
Fill in the field and click OK to save or Cancel to discard. After this you will be able to use this template to create courses.
After this you will see a notification message informing that the web site is successfully saved to the solutions gallery and can be used to create sites based on this solution. From this message you can go to the solutions gallery by clicking the corresponding link or return to the site administration page by clicking the Ok button.
2. Create SharePoint Subsite using this template: go to Site Contents -> click the +New button -> select Subsite.
Fill in the fields and click Create to save or Cancel to discard.
3. Create Modern page: go to the Settings (gear icon) -> click Add a page.
4. Customize it if you want.
5. Go to the Site Contents -> Contents -> Site Pages in the bottom of the Contents' list -> remove the previous Course.aspx page
6. Rename newly created page to Course.aspx
Click on the three dots next to the Course.aspx and select Make homepage.
Make a created template as a default.
How to delete created template
Please be aware: To deactivate templates you must be a site collection administrator.
To delete a template click on the Settings (gear icon) -> Site Contents -> Site Settings ->in the Under Web Designer Galleries block click Solutions -> Deactivate the selected template first and then delete it.