First of code redemption is done through the arc launcher nowadays, you will need to download this from the developers site arcgames.com
(or perfectworld, which is the distributor). In that launcher will be an option to redeem your code (cd-key) from a dropdown menu in the topleft corner.
Now about the content:
This is a great dlc to have for veterans and new players alike as it provides a significant advantage to all your characters. Not only does it allow you to create a badass looking dragonbron character, it even gives you one race change token so you can racechange one of your existing characters
+ dragonborn are one of the best races if you are into min/maxing
+ you get a big bag for inventory space on all your characters (bag space is hard to come by in the game)
+ you get a great artifact which will net you a cool breath weapon attack and stats (more so in the early game due to scaling of the stats)
+ a ring for every character that improves as you level
+ an extra character slot to start your new dragonborn right away
+ 2 sets of fashion gear ( for if your normal combat gear looks butt ugly you can just switch to the fashion overlay and you will look fancy ^^ )
+ a onetime assortment of enchantments and useful glyphs for when you've reached maximum character level
So if you really like playing the game and think about doing so for at least an extended period of time I would recommend buying this pack. Great extras (if only on looks alone ^^ ) for a reasonable price. Remember that the original game is free to play, so this would be a one time purchase to make that experience a little more enjoyable.