I taught it to myself. Actually I started pixelating before I even knew what it was. A friend of mine gave me a program called Gamemaker a longgg time ago, it came with a sprite package and a tutorial. I read through the tutorial, and while coding it, I thought I could make my own sprites. So I made a spaceship in paint, which I pixelated. And I also made balls which you shoot, in paint(without transparent backgrounds though).

The game never got anywhere btw lol. But that was the first time I pixelated. After that I got into RPG maker, which of course I had to make my own sprite sets for aswell :3

That was some nice practise^-^