Something habitable is appropriate to live in. If you're having the wood floors of your house refinished, it might not be habitable until they've completely dried.
Earth is a habitable planet: Mars isn't. In other words, humans can live comfortably on Earth, since its atmosphere has air we can breathe and temperatures we can tolerate. While many of us live in perfectly habitable homes and cities, there are also people whose living situations wouldn't be considered habitable by most of us. In Old French, habitable means "suitable for human dwelling," from the Latin habitare, "to inhabit."