Trying to understand mix and webpack as a begginer

Hello there guys i was looking for ways to increase performance on my laravel app and i heard some good things on webpack and since laravel have made a turn on it with its new version i would like to ask about how it is distrubuting javascript or even sass.

As i saw in some posts people say that webpack can bring javascript forward on demand like an app.js 32K on one page and on other 23k. Is this correct? If it is how can i do that with mix?