How do I add a html file to a website through cpanel with template?

The file uploads but does not do so in the site's template

[Automotive site]

I can upload a file through cpanel for the appropriate site after saving the file in notepad, but unfortunately when I visit the web page after uploading it the page just looks like a notepad page and does not show with the site's template.

When I go to the editor in the cpanel, the page just has the article but none of the code while all other pages have code. How do I upload the page to include the code?

I bought the site a while back and is a html site. I usually don't come across this problem since all my other sites are in Wordpress.

By the way, I am a person with very limited technical know-how as far as code is concerned.

[rocknbil]

If you're editing in NotePad, it is most likely saving it with the default extension of NotePad - txt. Save it with an .html extension.

File -> Save as
In the "Save As Type" drop down select "All Types"
specifically assign the .html extension in the file name: "index.html"