Oracle Approvals Management (AME) is a self‐service Web application that enables you to define business rules governing the process for approving transactions in Oracle applications that have integrated AME.
Here is very simplified way to explain AME and its usage in Oracle R12
https://drive.google.com/open?id=0B4AbEr3fAlmibXNvRUllYThNTVk
Videos links are here-
Oracle Approvals Management (AME) to Enhance Organizational Productivity
Oracle Apps Training – Configure AME Roles in R12