In the process of designing your HID class device, you also collect the data items into groups called Reports.

Once the data is completely specified, you encode this information into tables of numbers called “descriptors,” which the PC reads when you plug your device into a USB cable. The information encoded into these descriptors enables the PC to figure out everything it needs to know about the device and the data it will send and receive. No custom device driver is needed.

(Yes, this is a lot of work to do. That's why HIDmaker FS does it for you!)