one by one.
At the top of the screen there's a guide to tell you which numbers correspond to which colors. After choosing one of the colors, you tap on the correct cells to add a splash of color. Then, once you've finished, you can share the result on any social network you like.
PixelArt: Color by Number is a great 'pixel art' app developed by the team behind Picsart, which is known for its work on other photo editing apps. And just like their previous work, this app is also a home run in terms of quality.