Getting your React Native simulator up and running is notoriously tricky.  If you get any error messages through the next dozen sections or so, check out this article I wrote specifically to help troubleshoot issues in this course:

https://rallycoding.com/blog/troubleshooting-react-native-startup/

That post lays out a few common different error messages and some solutions for each.  I recommend you open up this page and keep it open for the next couple videos - at least until Lecture 20.  Most errors will usually pop up by Lecture 20, if not sooner :)