Upwind means towards the place the wind is coming from — so if you walk upwind, the wind is blowing into your face. Downwind is the opposite: the wind pushes at your back, and anything carried by the wind, like smoke or smell, travels downwind. This matters in real life more than students expect. A hunter or a wildlife photographer stays upwind of nothing and downwind of the animal, because an animal downwind of you will smell you. If there is a fire or a gas leak, you are told to move upwind, because the smoke goes the other way. Sailors use it constantly: sailing upwind is hard work and means going in zigzags, since a boat cannot sail straight into the wind. The word works as an adverb ('we moved upwind') and as an adjective ('the upwind side of the building'). When you name what you are measuring from, use 'of': 'stay upwind of the smoke', 'the village lies upwind of the factory'. It is a plain, practical word — not formal, but you mostly meet it in sailing, flying, hunting, farming, and safety instructions rather than in ordinary conversation.