PayPal has a number of different services, many of which are quite similar in terms of what they do. Their core services, PayPal Payments Standard and Express Checkout, are available to both free and premium shopping cart account holders. PayPal Payments Pro, Payments Advanced, PayFlow Pro and PayFlow Links are only available to premium account holders.
Each method of integration has slightly different setup requirements, just follow the instructions on the PayPal page in the cart setup.
PayPal Payments Standard
*Available to Free and Premium accounts
Using their standard method of integration the cart simply saves the order and then directs the customer to the PayPal website to pay for the entire cart contents as a single item. The order still remains listed in Admin even if the customer abandons the transaction when they get to PayPal.
There are some limitations when using the standard method of integration. In particular they only accept a very short description of the goods that are being purchased via their Web Accept system. Although the cart tries to push it’s contents into that description it may be cut off. You also need to setup either the IPN or Auto-return if you want the cart to send you an email when the customer pays.
Express Checkout
*Available to Free and Premium accounts
Express checkout is really just an alternative method of integration for Payments standard. Similar to the standard method of integration but with slightly tighter integration with the cart. The customer is passed over to PayPal to sign-in but is then returned to the cart to complete their final checkout phase.
Express checkout is the best solution if you sell goods which are delivered by being downloaded from the internet. It is also an excellent choice if PayPal is your only payment method.
PayPal Payment Pro
*Premium accounts only
PayPal Website Payments Pro is another so called all-in-one solution that allows you to accept both credit cards and PayPal payments. Buyers paying by card do so on a page which is not branded by PayPal. It is in effect, a real card payment method, there for people who choose not to pay by PayPal!
It is part of your agreement with PayPal that if you use Payments Pro you also use Express checkout although this appears not always to be enforced or encouraged by their own support staff.