Q: I have a iTunes card with 9.10 credit still on it.  I last used this card February 2013  How do I use it now in January 2014

I have a iTunes card with $9.10 credit on it.  I last used this card during the month of February 2013.  It is now January 2014 but I do not know how to use my card to make a purchase.  I am looking for help with this problem