After registering, you will receive a confirmation email at the email address you entered during registration from email@example.com. Click on the link in the email to confirm your email address.
If you have recently registered but can't find the confirmation email in your email inbox, please read Why haven't I received my confirmation email?
If you can access your account but no longer have the confirmation email, you may instead click the link in a password reset email message to confirm. Either click "Reset Password" in your Account Settings or from the edx.org log in page, click Forgot my password. Either will send the reset message to your registered email address.
Clicking the link in the password reset message will confirm your email. (You don't have to reset your password.)