Hulu has a free tier. The avialable content is more limited than a full subscription, and you have to watch a lot of comercials; but it's free and legal.
Some of the network apps like ABC, CBS, etc have some free content in their apps. This usually includes the last few eppisodes of one or two popular shows.
There are several other apps that offer comercial supported or completely free shows. You won't find much in the way of current TV series or popular movies; but there's plenty to watch if you're not picky. YouTube, if nothing else.