Something inhabitable can be safely and comfortably lived in. After a major fire or a flood, it can take some time to make a house inhabitable again.
The earth is inhabitable, but Mars is not. Your house is inhabitable, but your mom's pickup truck isn't really inhabitable. If you can inhabit, or live in a place, it's inhabitable, from the Latin inhabitare, "dwell in." An earlier definition of inhabitable meant completely the opposite: "not able to be lived in," from the roots in-, "not," and habitable, "fit to live in."