how to show custom errors in C# MVC

Hello vipin, in order to implement custom error page, first you need to add these lines in your web.config file

<!--Add this within <system.web> tag-->
<customErrors mode="On" defaultRedirect="~/CustomError" >
  <error statusCode="404" redirect="~/CustomError/NotFound" />
</customErrors> 

as you can see we have made customErrors mode  'on' now,  second thing which you need to do id create Controller(CustomError) and NotFound action method in it

public class CustomErrorController : Controller
{
    public ActionResult Index()
    {
        return View("Error");
    }

    public ActionResult NotFound()
    {
        Response.StatusCode = 200;
        return View("NotFound");
    }

    public ActionResult InternalServer()
    {
        Response.StatusCode = 200;
        return View("InternalServer");
    }
}

Now this will redirect to CustomError page but it will show you Error URL in it, so to remove it use, this instead

<!--Turn off custom errors-->

<customErrors mode="Off" />

<!--Then in system.webServer-->

<httpErrors errorMode="Custom" existingResponse="Replace">
  <remove statusCode="404" subStatusCode="-1" />
  <error statusCode="404" path="/NotFound.html" responseMode="File" />  
</httpErrors>

For detailed article, check Custom Error pages in ASP.NET MVC

that's it, you are done.