Amazon integration using API-
To test the various APIs, you can use the sratchpad. The link to it is- https://mws.amazonservices.com/scratchpad/index.html.
There are many API sections available like Feeds, Reports, Orders, Sellers and so on. Inside every section there are list of Operations which one can use to get the XML response.
Amazon integration using Import/Export Report-
Amazon gives several tab delimited reports like Unshipped Order Report and New Order Report. These reports can be used to import order into OpenERP. Once shipped, an export report can be generated from OpenERP which updates the tracking number and shipping service used back to Amazon.
The advantage of this approach is that it is faster since the system does not has to communicate over the internet. However,human intervention is required to manually import and export orders.