They detect the kind of app and then basically do everything required to build and run that app from pushing a repository. So it'll detect that it's a NodeJS ap

They detect the kind of app and then basically do everything required to build and run that app from pushing a repository. So it'll detect that it's a NodeJS application because there's a package.json file in the root and essentially: install node modules, run the build script and then do npm run start to run it. All you need to know how to do is: supply a build + start script and push your repository and now it's built and running in the Cloud to scale from 0 to unlimited. It's basically Heroku but buildpacks are a standardised way to do it on any Cloud.