I have never used one before. Do I have to go to their site and redeem this first, then come back here and use it or do I get the pin from the back of the card and use it here first?

Once you have the card go to the Cash Shop. On the page where you buy credits will be an option to input your code, rather than use PayPal. =)

Thank you very much! As always the administrators of this site are awesome.