Advection is the transport of an atmospheric property from one place to another by the wind.
Here, I'll be talking about temperature advection. In most areas of the United States, the temperature tends to increase if the wind is from the south, and the temperature tends to decrease if the wind is from the north. Of course, if temperatures are not warmer to the south, the mere existence of a south wind will not cause the temperature to rise. Similarly, if the air is warmer to the east, an east wind will cause the temperature to rise. Instead of relying on rules for wind direction, which work only part of the time, meteorologists look directly at the pattern of temperature and wind on weather maps.