It did just need to already have an OS on it. I didn't know that, but now it works.

I just got a new Raspberry Pi 3 and i'm trying to set it up now (mostly for Pi Hole). It has a micro SD card (FAT formatted). The only HDMI display i have is an Onn Roku TV, which doesn't detect the Pi plugged in over HDMI. It acts as if nothing was plugged in to the HDMI port.

The SD card in the Pi does not yet have an operating system. I have a Debian installer flash drive and i was planning to do that from the Pi.

I'm not even totally sure the Pi is on, because without a working screen all i have is the red power indicator light.

Is this a known issue between RPI and smart TVs? Am i just not turning it on right? Does it just need to already have an operatng system to boot into?

Yea, I think you just need to finish setting up the sdcard then boot it up. The tv isn't detecting a signal, so it's not displaying anything. Rpi isn't sending a signal because there's nothing to send.