Paint.net is a program where you can make images looks awesome.
1. Do whatever you want! edit a picture, make a virtual painting, etc.
2. Pretty much like any other painting/image programs. get a tool and start drawing something, or maybe open up an image to edit it.
3. Layers are... well, layers. they don't mess up things you do.
here are the features : http://www.getpaint.net/features.html
i swore there was a site about the tools in paint.net