How do yarns (details) become available on RavelryÉ

Hi so I was curious does anyone know how yarns and the details about them end up on Ravelry? Is it the designer? the brand?

My local yarn store has just release a new yarn that I want to buy but it's not on ravelry. is it just a matter of time? Or people who buy the yarn create the yarn on the site? How can I stash the yarn if it doesn't exist on the site?

Just curious if anyone knows the answer to this.

Thanks!