Search is your friend, and these are not the help forums. but since you are wet behind the ears, while you are in game go to the c-store and look under special unlocks. Thank you for flying Air Capulet
Make sure you are logged into the site and go to the front page. Under "Support" there is "Redeem Key". Enter your key there (usually it is on the back of the instruction manual or the slipcase for the installation CD). It's a 25-digit code. Make sure to enter it exactly as printed.
Once you have done that go into the game, the item is either automatically available (if it was linked to the version of the game you bought (Collector's Edition, DDE, etc) or the vendor (Best Buy, Gamestop, etc) you bought it from) or check the C-Store ingame (upper right there is a vertical row of icons. Click the downward pointing triangle ("Other options") and a drop down menu with open. Click on C-Store and click on the tab for Unlockables (I forget if that's what it is called. If you have any special unlocks you should have two tabs. One for the actual store and one for your special unlocks). Find the bonus item and click on it and then the "Claim" button. Special unlocks are available for all characters on that account usually (but you may have to unlock it individually for each character).
It has been awhile since I did this so this may be slightly generic sounding.
Note: uniforms options (and I think special races (Joined Trill, etc)) are automatically unlocked and in the character creator so check there first and if you don't see it, do the C-Store claim thing I described above.
Hope this helps (I'm doing it off the top of my head)!