Fusion 360 uses that same A360 hub system for it's data. If you're asking how to access the files/folders/projects/hubs through the Fusion 360 API (that's the forum you're in), you get in through the dataFile object, which you can get at through, e.g. Application.activeDocument. From the dataFile you can go up the hierarchy to access dataFolder, dataProject, and dataHub. The dataFile object has a property (id) which is what you need to then access that same resource through the Forge API.
If you're asking how to find those files through Forge API in the first place, you might have better luck on another forum? There are a couple of people kicking around here who use Forge, too, but I get the sense it's a minority. From the little I've done with it, I know you need to be using the Data Management API. It's the same hierarchy, so from hub you can get all the projects, and from a project, the top folder, and from a folder you can get all its contents, and some of those returned 'items' will have the extension type items:autodesk.fusion360:Design, which are what you'd consider the 'main' fusion 360 files.
Does that give you a place to start?
