You can create an account at any time, either before placing an order or directly during the purchase process. All your orders are saved and remain accessible from your account.
If you forget your password, simply use the "Forgot your password" function to set a new one.
If payment was made using the "Pay with PayPal" button in the shopping cart, the account was generated using the email address for your PayPal account. In this case, you will need to reset your password in order to access your account.