If you go on amazon for example and search for homeplugs you should see reviews on each item, google a lil about more information about them and perhaps watch youtube videos about them in generl or ones you think you’re interested in.
I’ve never used them myself but i believe you buy atleast a set of 2, one goes near your router at the power socket and you connect ethernet to it, plug another one in by the place you need it with ethernet coming from that and it runs over the electrical wiring in the home avoiding the need for extra long ethernet cable trailing everywhere. I’ve read they don’t work well with multiplug extensions but i think that’s more the ones that have surge protection which interferes with the signal.
The cause of the freezing could be caused by a number of things i guess, if the signal on wdtv is that weak when streaming it could be that, it could be the source you’re streaming from or even the speed of your connection especially if many devices are using the internet at the same time.
Powerline adapters is another term used for these plugs.