brew start react native code example

Example: react native new project mac

// Select a folder whereyou want to save the project
//go into that folder

cd React_Native_Projects
//to avoid some future problems when starting the simulator, i installed cocoapods in the general folder for all the projects (i didn't have it installed)
sudo gem install cocoapods

//create the new react native project
react-native init react-project //project with the name 'react-project'

//go into the project folder
cd react-project

//you can now lauch the simulator
react-native run-ios

//if you run into the error 'Failed to build iOS project. We ran 'xcodebuild' command but it exited with error code 65'
//try doing this
cd ios
pod install
rm -rf build/
cd ..
react-native run-ios