Please make sure that your account is verified before login. You will get an email after you register with verification link. Your email id is your user name. If you forgot your password then click on forgot password and enter your email id and submit. You will recieve new password.
Login and go to "Account". Then go to profile and click "Change Password" button.
Click on "Subsribe now" and select the desired plan for you. Click "Buy Now" and continue with the payment process. After successful payment you can view your subscriptions in your account.