He’s using parallax (I think) which you probably shouldn’t be worrying about.
[quote=""]
Not parallax. Basically, take the snowflake class and drop the sine and spawn a bunch of them with random velocities. And all with a random small gravity pulling them down. That is the basic idea of particles which are simply to start with but hard to get looking good.
If you would like I can give you the source but it might be a bit much.

i learn better with examples