Program Substitution
The world is fill with many graphics programs some free, some not free. Photoshop, I must say is an AMAZING program however, I refuse to pay money for graphics programs (unless it is super cheap XD). You must be thinking, well what are you supposed to make graphics with if you only have MS Paint you can't afford Photoshop or Paint Shop Pro? There are however other alternatives!
GIMP
GIMP stands for GNU Image Manipulation Program or for all you non-techies out there its basically a FREE Image editing program. This program does not exactly match up to Photoshop and Paint Shop Pro, but its pretty good. I use GIMP for 99% the graphics I make. GIMP, like Photoshop allows you to download brushes and use them. They have a fuzzy, rectangle, ellipse, and free hand select tool. One pretty cool tool that I'm pretty sure most image editting programs have is the path tool which helps with lineart. It obviously has most of the basics like color picker, zoom, move, rotate, text, fill, gradient, pencil, eraser, airbrush, etc. However, the downside to GIMP it doesn't have the basic shape tools, you have to use the rectangle select and color in the selection so that you can have a specific shape. It has some pretty basic effects but overall it is a pretty good program.
Paint.NET
Paint.NET is a image editting version of Microsoft Paint. It has many of the same effects and tools as GIMP but this time it comes with a shape tool! The fill tool they have is pretty cool because you can make backgrounds in a snap. Paint.NET however, doesn't have a build custom brush creator like GIMP. It has you install a plug-in and upload the brushes yourself and it takes forever where as in GIMP, the custom brush saver is default in GIMP. Paint.NET is a reasonably good program but it isn't as good as GIMP.
My recommendation
I personally find both programs useful. If you are looking for some free image editting software feel free to download both. I use GIMP more often than I use Paint.NET but at times I use Paint.NET to cover up for the things that aren't available in GIMP, vice versa.