MakeCode is Microsoft's drag-and-drop code editor, and it's about the easiest way to get your pixels showing color.   

Click the appropriate button below to go to the MakeCode strandtest project. Click the Download button on that page, and a file called circuitplayground-strandtest.uf2 (for Circuit Playground Express) or maker-strandtest.uf2 (for Gemma M0) will download to your computer.  

Plug your Circuit Playground Express into your computer via a USB port and double-click the tiny "reset" button in the center of the board. All the onboard lights will turn green, and a drive will appear on your computer called CPLAYBOOT or GEMMABOOT. Drag the file you just downloaded onto this drive.  

The pixel you have connected will light up in a succession of colors followed by a rainbow animation.

Note: MakeCode will NOT work on a FLORA or GEMMA v1 board.  For those older boards you must use the Arduino code method.  However, Arduino will work on Circuit Playground Express or Gemma M0 as well as the older boards.