This is a rudimentary pixel art editor, to test your designs. Start by looking inside the project. There is only one sprite, called `pixel`. Check it's different costumes: they correspond the the colours you will be using in your design. Modify the colours at will. Proceed by setting values for the `rows` and `columns` variables. These values will dictate the resolution of your image. Press the green flag and you will see a uniform grid of pixels appearing. To set the current colour, click on the pixel that stands out, at the bottom right. Clicking on that square repeatedly circles through its colours (costumes). Clicking on any other pixel will set its colour to the current colour.
Thanks to NCCE for the original project Pixel art editor.