When there is higher demand for a good, i.e. if people demand 'more' of a ipod
the price of the ipod would increase, and because u would pay more for a ipod (because u demand it more) (by the price mechanism, price would increase to make 'rationing' work)
the supplier would increase the quantity supplied, therefore Q also increases
When the supply of ipod is decreased, the price of ipod would increases because there is less available ipod for the same amount of demand... again by the price mechanism, price would increase to make 'rationing' work. As the supply is decreased (at the same given demand), the quantity would decreases.
