It plugs into an open HDMI port on your HD TV and then it also requires a power connection that can usually be plugged straight in to the TV's USB port or the small power supply that comes with the device. Once it is connected and setup you simply stream content, videos and music from a device, to your TV. Currently the apps that are supported consist of Netflix, YouTube, HBOGo, HuluPLUS, Pandora, and GooglePlay Movies. You can also mirror stream right from Google Chrome from any PC, which means what you see on your PC's display in one tab of chrome is what you see on your TV. It is also cross platform, Apple and Android devices are able to stream. Keep in mind that to use this device with Netflix, HBOGo, and HuluPLUS you have to be a subscriber to each service. With GooglePlay Movies, you just have to purchase the videos or watch ones that are free.
I am absolutely amazed at how well this system works. There is talk among the tech communities that there will be more apps available in the future. I can't wait to see what is next for this little device. The price of a Chromecast is $35.00, I picked mine up at Best Buy and I have noticed them at quite a few of the other stores I frequently visit, for the same price. This would make a great stocking stuffer for those tech enthusiasts in your family.
Another share, a video I really enjoy, by Phil Wickham recorded live by Klove Radio.