Why should you care?

URLs map to controller actions. Without controllers, your server would not know what code to run for /Cart or /Checkout.

See it live — copy this example

Create an MVC project (dotnet new mvc), add the code, and run dotnet run.

public class ProductsController : Controller
{
    public IActionResult Index()
    {
        return View();
    }

    public IActionResult Details(int id)
    {
        ViewData["ProductId"] = id;
        return View();
    }
}

Run Example »

Edit the code and click Run — like W3Schools Try it Yourself.

What happened?

• Controller base class gives you helpers like View() and RedirectToAction().
• The name ProductsController maps to /Products/...
• URLs by convention.

Try it yourself

1. Add ProductsController with Index and Details actions.
2. Create matching views under Views/Products/.
3. Browse to /Products/Details/42 and show id in the view.
4. Change text or labels in the example and run again — watch the browser update.
5. Break the code on purpose (remove a semicolon), read the error message, then fix it.

Remember

Controllers receive HTTP requests. Actions return IActionResult (usually View or Redirect). Class name minus "Controller" becomes the URL segment.