First, install dependencies with
$ npm install
Next, install webpack and webpack-dev-server globally
$ npm install -g webpack
$ npm install -g webpack-dev-server
Then, build with
$ webpack
You should now see a dist folder created in your project. This folder should contain two files: bundle.js and index.html.
Run dev-server using
$ webpack-dev-server
Open your browser to localhost:8080. You will see the page you are working on. Any changes made to .js and .scss files will update immediately using webpack hot module replacement.
If you make a change to index.html, you will have to run $ webpack to build again.