what is it ,when thay say to hunt down win

It has to do with the animals picking up your scent which you do not want.  So whichever way the wind is blowing it should ‘hit’ the animals before you.  If the wind hits you and then the animals, the animals will pick up your scent.  For example, if the wind is blowing west to east you want to be east of the animal (this would be down wind).