Wikipedia says :
"Star Trek: Discovery premiered on September 19, 2017, at ArcLight Hollywood, before debuting on CBS and All Access on September 24. The rest of the 15-episode first season will be streamed weekly on All Access."
It seems to be running on "CBS All Access", whatever that is. Let me see....
Their site offers 1 week of viewing at no charge.
"CBS All Access comes in two flavors, with commercials and without. The standard subscription costs $5.99 for streaming with ads, while the ad-free version will set you back $9.99 a month."