Custom Web Service in AX 2012

Hello,

 I have created new two tables and one form by using this two tables in AX 2012.Now  I want to create "Custom Service" with "Create","Read","Find" Operations and also add validation on that custom service.(eg Create SalesOrder by using SalesSalesOrderService.create)

Please Help me to create a CustomService with create Operation.

Thanks ,

Darshana.