There are a couple of ways to leverage the Excel Add-in with AX one using the tables as just a data source another using a prepared service. This allows you to make a more complex entity that you might want to save the user doing some work of joining data together and you prepare that for them. This video gives you a quick walk through of the basic setup, creating a service and using in the Excel Add-in.
This video was recorded with AX2012 R2 but the same concept applies to any release of AX2012. If you are using AX2012 prior to R2 then it’s worth investigating the upgrade to a later release for the Excel add-in as there was a lot of enhancement done in R2