SmartVault sends you an activation email when you create your account or when a SmartVault account owner invites you to join the account. Check your inbox for this email. The sender is firstname.lastname@example.org. Be sure to check your Junk or Spam folder as well.
If you can't find the activation email, you can have it resent by following the instructions found here - Resending the Activation Email or by contacting the SmartVault account owner who invited you.