CircuitPython is a derivative of MicroPython designed to simplify experimentation and education on low-cost microcontrollers. It makes it easier than ever to get prototyping by requiring no upfront desktop software downloads. Simply copy and edit files on the CIRCUITPY drive to iterate.
If you've already plugged your board into your computer, you should see a drive called CIRCUITPY. The drive will contain a few files.
If you have already plugged in your board, start by ejecting or "safely remove" the CIRCUITPY drive. This is a good practice to get into. Always eject before unplugging or resetting your board!
Follow this quick step-by-step for super-fast Python power :)
For more detailed info on installing CircuitPython, check out Installing CircuitPython.