Once you have the Arduino IDE installed or updated, you will need to set some parameters to get the right libraries, board definition file, and the TinyUSB stack.
In the Arduino IDE menus, go to Sketch -> Include Library -> Manage Libraries. You will need to ensure you have the latest versions of the following libraries:
You will need to test this on an Adafruit SAMD board such as the Circuit Playground Express, Metro Express M0/M4, Feather Express M0/M4, and others.
In the menu go to Tools -> Board -> Boards Manager. Type in Adafruit SAMD to search. It will likely pull up both the Arduino SAMD board package and the Adafruit SAMD board package. Select the Adafruit SAMD package and ensure it is at least version 1.5.3 or higher for TinyUSB and WebUSB work.
Finally, go to Tools -> USB Stack and select TinyUSB. If this is not selectable, update your version of the Arduino IDE. Switching the USB stack puts in TinyUSB instead of the default Arduino USB stack. TinyUSB has more features including WebUSB support.
The screen below shows the Arduino IDE with a Circuit Playground Express board. The CPX is plugged in and in bootloader mode by tapping Reset once or twice and seeing a circle of green lights.
See the settings circled in red.
Ok, that is all the configuration needed to work with the code in the two examples next.