The home phone for fiber optic, there is an optical cat, I buy a network set-top box can be used?

Of course you can use it, the hardware connection is shown in the picture above, which is a typical network structure schematic for home network, hope it can help you.

Note: After the router is set up, all devices can access the Internet through the router, and the TV has to be set up to input the video source, i.e., you need to select the video source from the AV terminal input or HDMI interface input.