How can I open my page without .html address?

I am a beginner, so sorry for this question.

the main page name is: index.html

and a second page is for example second.html

The issue: I can just open it on the browser by using the full name includes .html means: www.example.com/second.html

If I type just: www.example.com/second it is not possible to open the page.

Can you maybe tell me what I do wrong?