By default, YouTube plays videos from your subscriptions, but you can also select a category to play popular comedy videos, short films, music videos, news, travel videos and more. The interface doesn't work with a mouse, as you can only use the arrow keys and Enter to skip a video, select a category, search, pause or resume a video. YouTube Leanback will work well with Google TV's remote control, but you can also install an application like Air Mouse on your mobile phone.
Leanback is not the first YouTube interface designed for TVs: there's also YouTube XL, but the interface isn't fluid and there are too many options that get in the way.