If something is quiet and calm, it's still. After the noise of the city, it's peaceful to go camping in the woods where everything is still.
Things that are tranquil are still, like the calm surface of a lake or a sleeping baby. If you stand still, you freeze in place. Another meaning of still is an individual shot from a movie, an unmoving snapshot of a single scene. When still is an adverb, it means even now, like when you say you still love an old song or you still remember the kindness of your kindergarten teacher.