These keys will secure your spot in TERA's Closed Beta Test 4 for North American players only, which runs this weekend, beginning on March 23rd. Just click the button below, claim your key, and then copy and paste it into the appropriate section of your En Masse Entertainment account, which you can create at the official site. After you've verified your email address, click the "enter code" button on the right side of your account window and submit your key. You can download the TERA client via the button on the account overview tab.
Don't forget to have fun!