How do I create a view controller file after creating a new view controller?

Correct, when you drag a view controller object onto your storyboard in order to create a new scene, it doesn't automatically make the new class for you, too.

Having added a new view controller scene to your storyboard, you then have to:

1. Create a UIViewController subclass. For example, go to your target's folder in the project navigator panel on the left and then control-click and choose "New File...". Choose a "Cocoa Touch Class":

   

   And then select a unique name for the new view controller subclass:

   

2. Specify this new subclass as the base class for the scene you just added to the storyboard.

   

3. Now hook up any IBOutlet and IBAction references for this new scene with the new view controller subclass.