To sign in click on the login button at the top right to take you to the log in page. To log out after signing in click on the logout to log out.
If you forgot your password click on the "Forgot Your Password" link next to the log in button, and put the email address associated with your account into the form before hitting submit. After you do that an email with a link will be sent to you. Go to that link and you'll begin the process of making a new password for your account.