After adding a product to your basket, simply click on 'Checkout".
You will be given the option to pay with PayPal under "Pay with my PayPal account"
OR
You will be given the option to make a card payment. Continue to the PayPal log in section and then instead of logging into Paypal simply click on "Pay with a debit or credit card" and then follow the instructions given.
Or if paying with PayPal you can simply click on the 'PayPal checkout' icon below the Checkout button.