As with your earlier questions, the answers are all in the doc files. Frankly if just exploring an example folder is not enough to see what a GRC resource file is or that apx is an add-on, you may not have the level if curiosity required to do API work as often detective skills beyond such obvious things are required.
One of the forum moderators • AC 25 USA and earlier • MacOS 11.6.2, iMac Pro
In Visual Studio 6.0 you can create a new ArchiCAD Add-on with the provided wizard. Select the API DevKit folder and (optionally) add support for dialogs & input/output. We won't need them for "Hello World".
I didnt really understand what this order means, and how can I open a new ac add-one file in Visual studio.