I’ve done posts in the past about the punchOut flow. This one is basically the same but using the cXML punchOut protocol handler for AX2012. To the user they won’t see any difference as they shouldn’t because the protocol is what passes the data between the procurement site and the suppliers site. In this example the external site is Staples but it could be used with many different supplier sites that support cXML.
Here is a quick overview.
For notes on downloading the cXML punchOut protocol for AX2012 see this post