You don't need to have an account with PayPal in order to make a purchase. PayPal will allow you to pay with a credit or debit card and without a PayPal account.
When you get to the checkout screen choose the "Pay with a Debit or Credit Card" option on the bottom when you see this screen
After choose this option you will see the screen below to enter your credit card information.
In some cases, PayPal won't allow you to checkout as a guest based on various reasons..
PayPal will make a decision to not allow guest checkout in some circumstances depending on a number of details e.g. customers browser, cookies, locale, IP etc.