An email was sent to the address you provided with information about your new account and contained a link to finish activating your new account. You may need to check your spam folder if you don’t receive the verification email.
When you click on that link, your account will be activated, and you will be returned to this site to log in with the credentials you created when you registered your account. [If you forgot to write down the username and password you created at registration, not to worry. You will receive another email after activation that will contain your username; you can always reset your password using the “Forgot password?” option on the login form.]