This was being discussed in the anime thread, but this is definitely something that deserves its own thread due to the gravity of this tragedy.
CW for descriptions of violence and the aftermath of the fire:
For those who want to know more about the studio, Sakugablog did a good article about their history last year:
Please try not to speculate about the attack. And though it may be best to wait to donate until there’s confirmation of that Kyoto Animation will accept the money, Sentai Filmworks has set up a fundraiser to help the victims. It is also possible to support the studio directly by buying digital goods such as wallpapers from their store, here’s a guide on how to do that.
Update: KyoAni now also accepts donations directly. I imagine this also means that they’ll accept Sentai’s fundraiser. Also, while they do accept payments from overseas, keep in mind that those likely include heavy fees.