Here are tutorial to let you know how to setup PayPal and make PayPal works properly in your website.

1) Log into paypal.com by your paypal account.
2) Go to my profile page ==> Selling tool, like this screenshot

There are 2 section should be updated.
1) Instant payment notifications
Enable Instan Payment and set url is: yourdomain.com

2) Website preferences

• Auto Return for Website Payments: On.
  Return URL:http://yourdomain.com/process-payment/
• Payment Data Transfer: On
• Express Checkout Settings: On