Sample Global.asax for a webforms project

ApiModule.cs

// You could use a module to describe all the dependenices in some api dll and make
// it easier to load all components from that project.
public class ApiModule : Module
{
  protected override void Load(ContainerBuilder builder)
  {
	builder.Register<UserManager>().As<IUserManager>();
	builder.Register<QasAddressService>().As<IAddressSearchService>();
    
    	// Anything else required.
  }
}

Global.asax

// Sample global asax that creates a container for the web application. It creates
// a container via the 'container builder' and components are registered in it 
// directly or by 'modules' that bring common dependencies together.
public class Global : HttpApplication, IContainerProviderAccessor
{
  // Provider that holds the application container.
  private static IContainerProvider containerProvider;

  // Instance property that will be used by Autofac HttpModules
  // to resolve and inject dependencies.
  public IContainerProvider ContainerProvider
  {
	get { return containerProvider; }
  }

  protected void Application_Start(object sender, EventArgs e)
  {
	// Build up your application container and register your dependencies.
	ContainerBuilder builder = new ContainerBuilder();
	
	// Register a type directly. This is a basic registration that doesn't
	// control lifetime or whether the component is 'IDisposable'.
	builder.RegisterType<SomeDependency>().As<ISomeInterface>();

	// Structure some dependencies in a wrapping 'module'. See the module code
	// for a motivation for this.
	builder.RegisterModule<ApiModule>();

	// Once you're done registering things, set the container
	// provider up with your registrations.
	containerProvider = new ContainerProvider(builder.Build());
  }
}