Sales Order Web Service Creation

Hi Everyone

I am new in AX I have a requirement to create a custom web service for creation of sales order/ purchase order. Can any one explain the detailed steps to complete the task?

Thanks in advance!!

Unfortunately you forgot to mention your version of AX (please always attach a tag with the version, such as AX 2012), but you mentioned AIF and AIF always had standard document services for sales and purchase orders. Why would you create another services for the same purpose?