Roku is a company that manufactures digital media players. The Roku player is a small device that connects to your TV and allows you to stream content from the internet. Roku players come in different models, some of which have built-in WiFi and some of which don't. The model with built-in WiFi costs more, but it's worth it because you'll be able to connect to the internet without having to use an Ethernet cable.
There are several different brands of TVs that have built-in Roku players. Some of the most popular brands are Samsung, LG, and TCL. You can usually find these TVs at your local electronics store or online. If you're not sure which TV has built-in Roku, you can always check the product description before you buy it.