How do I set up PayPal with Marketpress

Hello

I need to set up a paypal gateway in order to take payments. The site is a redesign for older site that used a different ecommerce system that accepted the normal paypal payments. I switched to marketpress for the new site but I see that it only allows for PayPal Express and PayPal Payflow Pro. Could someone please show me step by step how to set up PayPal express. I need to get this working asap.

Thank you