This is a very broad question. Can you be more specific about the contents of your text file and where you would like to see the data populated in AX? For example, is your text file a csv of customer data? Vendors? Inventory Items? This will help us guide you down the right path
The AIF can be used in many ways, either via netTCP WCF communication to a Windows C# application developed in MS Visual Studio, or you can also use a File Adapter to work with a folder that you can drop the import text file in to and will be seen and utilized. If you opt for the FIle Adapter, you will need to either set up Value Mapping on an inbound port, or setup a custom Transformation to convert values in your file to their “equivalent” value in AX prior to the service populating the data ( ex. your file has a customer Group called “Customers” but needs to go in to the “Client” group setup in AX, you will transform that here ).