Show streaming video to a LG Smart TV I'd like to broadcast videos seen on common web sites (like CNN and such) to my LG Smart TV. 

I know I could use dlna or protocols like that to stream a local video file on the TV, but haven't yet found any way to play streaming videos. 

Any idea?
There are multiple ways you can do this.

Some TVs have a built in casting functionally. Since your TV is a Smart TV, there is a chance that you TV could support this.

You could buy a Chromecast. It costs $35 for non-4k, and $69 for 4k. You can use Google Chrome to cast webpages, but some webpages or apps support it natively. This works on both mobile and computer.

You could also buy an Apple TV. The latest one costs $150 for 32 GB and $200 for 64 GB. You can cast from both iOS and macOS. You can use AirParrot($20) to airplay from Windows and older macs.

Lastly, you can use the Amazon Fire TV Stick($40) or the Amazon Fire TV($90). This would be my last choice, because it doesn't support casting. Instead, you would use apps. The bonus is that you can use the Alexa remote, sort of like the Siri remote.

I would choose the Chromecast, because it isn't very pricey, but it enables you to cast anything to your TV.