To use the codes you must login to the SWTOR website account page and select "Code Redemption" in the left hand menu (or use this link). Click the "Enter a Code" button on that page and copy and paste the code in. Some items are sent via the in-game mail system whilst others are applied to your account the next time you login.
If you know of any more then please post them below and I'll update the list. Let me know if any have expired.