Create your account at WorldPay.com then click on Admin->Extensions->payments
Locate Worldpay , click on Install if it is not installed then click on Edit and a form will display with following fields.
Merchant ID: Type merchant ID.
Payment Response password: Create Payment Response password.
Test Mode: Select Production if you are in production.
Total: The minimum amount to enable the order being processed by Worldpay.
ORDER STATUS: Apply this payment method to orders that have this order status.
GEO ZONE: Select a zone if you want it only available to a certain zone, otherwise leave at ALL ZONES.
STATUS: Select ENABLED to allow customers to select this method; or DISABLED to hide it from customers but keep it available to you in your private Admin.
SORT ORDER: If you are offering customers multiple payment methods from which to choose, and wish this method to be displayed first, enter a 1. To display second, enter a 2, and so forth.
Click the SAVE Button when you are finished setting up.