I feel like I'm missing something in regards to how this will work. I've already got a Chromecast Ultra and I already have PS4 controllers. I will be satisfied

I feel like I'm missing something in regards to how this will work. I've already got a Chromecast Ultra and I already have PS4 controllers. I will be satisfied with 1080p gaming quality. Can I try this out for free or do I have to purchase a title? Do I need a laptop/phone that is casting to my TV? Can I use my PS4 controller? If so, what would it be connecting to - my laptop/phone?