You can use any Android or iOS smartphone and/or tablet. You download the Google Home app to make everything work.
As for what you can stream, that depends. First, your TV doesn't have to be Smart, but it must have a HDMI input. Next, whatever you want to "cast" to your tv must have that option available within the app. Apps such as Hulu, Netflix, NHL Center Ice, You Tube, etc, all have a cast option. You simply start watching on your phone, then hit the cast icon and boom, it is on your tv. Your phone/tablet screen can power off and the picture will still cast to your TV. You can even multitask and use your phone/tablet for other things while watching TV.
Pretty cool stuff.