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 choosing 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 related to details like customers browser, cookies, locale, IP etc.