React Native is a popular and widely used cross platform android and ios app development and developed by facebook. before getting started make sure latest nodejs, npm, react native cli and android emulator running. then navigate to terminal and run the below command to start a new react native project

react-native init helloworld

Note: helloworld is project name

then navigate helloworld project folder by cd helloworld 

then by view the default react native project by run

react-native start

then in new terminal tab again run the following command to view in android emulator

react-native run-android