It is necessary to understand the client-side and server-side of web applications and what can be done either side. With respect to web applications, your client is the browser and your server could be the web server/application server.
The browser side is whatever that happens in your browser. It is the place where your JavaScript code runs and your HTML elements reside.
The server-side is whatever happens at the server at the other end of your computer. The request that you fire from your browser has to travel through the wire (probably across the network) to execute some server-side code and returns the appropriate response. Your browser is oblivious to the server-side technology or the language your server-side code is written in. The server-side is also the place where your C# code resides.
Let us discuss some of the facts to make things clear:
Fact 1: All browsers can only understand HTML, CSS, and JavaScript, irrespective of the browser vendor.
You might be using Internet Explorer, Firefox, Chrome, or any other browser. Still, the fact that your browser can understand only HTML, CSS, and JavaScript holds true. It cannot understand C#. It cannot understand Java. Nor Ruby. Only HTML, CSS, and JavaScript. This is the reason why you can access the web applications, built using any technology could be accessed by the same browser.
Fact 2: The purpose of any web development framework is to convert your server-side code to HTML, CSS, and JavaScript.
This is related to the previous point. As browsers can only understand HTML, CSS, and JavaScript, all the web development technologies should convert your server-side code to HTML, CSS, and JavaScript so that your browser can understand. This is the primary purpose of any web development framework. This is true for whether you build your web applications using ASP.NET MVC, ASP.NET Web Forms, Ruby on Rails, or J2EE. Each web development framework may have a unique concept/implementation regarding how to generate the HTML, CSS, and JavaScript, and may handle features such as security performance differently. But still, each framework has to produce the HTML, because that's what your browsers understand.
