Paint.NET :: Design Characters For Games

So, i would like to become a Graphic Designing or atleast keep it as a hobby. More likely, i would like to design characters for games, in the beginning 2d sketches and why not 3d models. So, my first question is, what do I have to learn  first to become a decent graphic designer, how to start, and what should i focus on?
 
 My second question relates to Paint.NET. So, i've been experimenting with making sprites of images that already exist, by taking parts of them and putting them together, and changing colours and stuff. But now that i've tried making sprites of my own, i've got some problems of making a starting black and white sketch. I've been using the lines and curves tool but the curves are hard IMO to use. I would wanna know if i could copy somehow curves and reverse them, ill give you an example of why I want to do it.The head of the sprite would be cooler, if both right and left side would be symmetric.