There's more...

Once you have launched an app in the simulator, you'll be able to press the Run on iOS Simulator button without opening Simulator from Xcode. It should also remember your device choice. Opening Simulator from Xcode provides an easy way to choose your preferred iOS device to simulate. 

You can toggle between your React Native app and the Expo Developer menu, a list of helpful features for development, by pressing command key + M on your keyboard. The Expo Developer menu should look something like this: