Super simple. Either copy & paste or append the 'snowflake' object into your project. That's your new particle, and you're all set. There are some quick sliders in the settings just to adjust opacity etc, but apart from that it just works.

We don't use Eevee at our studio so I don't know if there's some quick adjustment to make it work in Eevee, but right now it doesn't create unique flakes outside of Cycles.