Well, it may depends on the style you're going for.

If this is pixel art, which i found relatively easy when having no big artistic background, i can recommend those youtube channels : AdamCYounis, Brandon James Greer, and Pixel Pete. I also hugely recommend the series of mini-tutorial over here, it's pixel art tutorial all in pixel art, and it's amazing.

If you're looking for other styles, i don't have ressources to learn. People already recommended Gimp and Inkscape (and Blender, you can do a bit of 2D in there as well, though it may not be the most comfortable way). I'd also add Krita, which is more meant for traditional drawing. It works way better with a graphics tablet though, but even a cheap one does the trick.