If the payee has enabled the Guest Payment option on his/her PayPal account, the payer can now complete a payment by simply using a credit card without having to register to PayPal. Once a user is redirected to Paypal.com he/she can pay with a Credit Card by clicking on bottom slider on right side of the screen.

NOTE: In EU countries, a maximum of 10 Guest payments are allowed per user after which user is forced to open a PayPal account.  If a user uses different email address then he/she can make another 10 guest payments. This is not a product restriction but part of EU regulations which will be lifted in near future. This restriction does not apply for North America and the rest of the world.