If you are looking to use AX for coordinating some of your purchasing of expense there is a lot of functionality in AX to control the process. Some of the things that you will need to setup are a category if you don’t want to track inventory related to the purchase and a GL account to post to. You can link the two through the inventory posting setup.
Here is a quick overview.
AX7 Build 7.0.4230.16130
If you are working with AX2012 you can get an overview here.