Who knows how to integrate a C# code to work on a website? Or must I always use JavaScript??

Answer 1

You can link C# and HTML together(or integrate C# into HTML) using the asp.Net, or using JS to 'run' a C# code is one way too, but some browsers with sensitive securities may prevent it. I recommend checking using search engines.

Answer 2

Use Asp.Net MVC or WebApi as backend and call c# methods from js using ajax.