Ambiance is describes as the character and atmosphere of a space.
And from time to time we may want a certain 'feel' for our home. We are all used to creating ambiance at home already. Think when it is Autumn time and the nights are dark, stormy and cold and we light a fire, dim the lights and hunker down under a cozy blanket to watch a film. That is creating ambiance. Or if we want to unwind after a stressful week so we light candles and take a long hot soak in the bath with bubbles. That is creating ambiance.
What's fun is that you can also further create the atmosphere you want by using fragrance to help enhance the vibe you are wanting.
Check out this handy guide for ideas on how you can influence the ambiance to a situation.