xcode simulator doesn't show anything (just blank)

print screen: https://s18.postimg.org/51vvdapqx/xcode1.png

The launch screen with "Food Tracker" is probably appearing for such a brief moment before the initial scene, which is supposed to be white and empty at the beginning of the lesson, is displayed that you don't see it. Continue with the lesson and you should find that the elements you're instructed to add to the initial scene will appear when the app is run.

OK, thank you. I'll continue. I don't see it and I just see blank. the brief moment must be 0,0000001s.

I've just looked at the tutorial again and my reply was incorrect. The launch screen will be displayed for long enough to read, but the tutorial doesn't instruct you to put a label containing "FoodTracker" in the launch screen. Maybe older versions of Xcode automatically create a launch screen label when a new project is started from an iOS app template, but my Xcode 8.1 beta 3 creates a blank launch screen, and I guess you're using Xcode 8.x. You'll soon learn how to add a label to a view, then you can add one to LaunchScreen.storyboard yourself.