Your shoe does not fit correctly. Blisters often mean that the shoe is rubbing places too much when you walk. If the shoe is too small, the shoe will be too tight and restrict your foot, in turn making your toes forced together and heels being rubbed. If the shoe is too big, your foot moves around too much in the shoe, making the shoe to cause blisters.
Answer:
Cooling down allows your body temperature, blood pressure, and heart rate to return to their normal levels. Stretching your muscles while they're still warm can help to reduce lactic acid buildup, reducing your chance of muscle cramps and stiffness.
Hope this helps :)