Painting: The brush will be on your mouse. Move your mouse to the bottom left to open the palette. You can change the number of dots with the slider. Changing this slider will delete all of your work. Use the B and N keys to navigate the 3 pages of colors. Click on the color you want to paint with. The brush may hide and it will tell you to wait, if so, keep your mouse on the color until the brush shows again, this is due to the color picker, it just lags sometimes. Click a dot to color it with the color you have selected. Press M to switch to the color of the dot your mouse is on. Press C to switch all the dots to the color selected. Press X to cycle through different colored backdrops. Saving/Loading: Press V to show/hide the save list. To save: See inside, right click on the list and choose export. The list will download as a text file. To load: Make sure the grid size is the same size as your code is for. See inside, right click on the list and choose import. Select your save code, and it will load into the list. click off the list and then press V once, and your picture should load.
@griffpatch for the color picker, the rest is completely me.