Note: Make sure you have completed the React Native - Environment Setup instructions till "Creating a new application" step, before proceeding.
First, you will need to start Metro, the JavaScript bundler that ships with React Native.
To start Metro, run the following command from the root of your React Native project:
# using npm
npm start
# OR using Yarn
yarn start
Let Metro Bundler run in its own terminal. Open a new terminal from the root of your React Native project. Run the following command to start your Android or iOS app:
npx react-native run-android
npx react-native run-ios