Either run the Java backend by using your IDE or by typing

mvn exec:exec

in the back-end folder. This will start the Java server at http://localhost:8080.

In the front-end folder, run

npm install
npm start

This will start the front-end server at http://localhost:3000. You can update the front-end code as the server is running in the development mode (i.e., npm start). It will automatically recompile and reload.