Follow the official instructions to set up React Native for your environment. For this exercise it is not necessary to build for ios if you do not currently own a Mac, though if you do we will expect you to have already installed XCode (with cli utilities). Developing for Android on Mac, Windows or Linux will require the Android toolchain and at least one SDK.
git checkout RNU_0723
npm install
cd ios
bundle install
pod install --repo-update
bundle exec pod installNormally npm run android is sufficient in most build environments to launch a metro server, compile via gradle and launch the app in an emulator. Depending on your environment it may be necessary to launch metro in a separate window with npm start and then build the app.
This requires a Mac and XCode, of course. npm run ios may be sufficient to build and launch an emulator, however it is sometimes necessary to open the ios/xola_dev_rn.xcworkspace project in XCode and allow it to build and launch from there.
If you can't get this to work, see the Troubleshooting page.