When you choose Paypal on checkout page, you will be redirected to Paypal payment page, where you can login your Paypal account if you have one. Or pay by Paypal Guest Checkout, where you can directly put in your credit card information and pay. The page is protected by Paypal and they don't share your financial details with the merchant.
How to Contact PayPal
If you run into any trouble or have any questions about PayPal's Guest Checkout, please contact PayPal directly.
PayPal's phone numbers are: 1-888-221-1161 (US), 1-402-935-2050 (if calling from outside the US)