Essay time!
Well there are basically two types of graphics out there: vector and raster. The type of program you use will determine whether your art is vector or raster. The main difference is in how the computer handles the lines that you draw. In a vector art program as you draw a line, the program will construct your line using 'points' (think of it like those connect-the-dots art books you had as kid). After the line is drawn, the collection of 'points' that make up that line is considered as a single 'path', meaning it's like an object you can move around freely, and it is independent from all the other lines. this means that if you drew a line and it came out all crooked, or not to your liking, you could either draw over it again to make it change slightly, or you can use your mouse to manually select the points and move them about. Of course because everything is essentially just a collection of 'points', this means that vectors can be resized to *any* size with no loss of quality whatsoever. (If I wanted to make a building-sized poster of Lingo Cider here, I could technically just export a 10 meter by 10 meter version of it and it'll look the same as it is now )
The downside of vector art is that because everything is made out of 'points', it's very difficult to just use a brush tool or something to 'shade' an object, because it'll just come out as a bunch of messy lines that overlap one another. In fact, I don't even have stuff like an airbrush tool, blur tool, smudge tool, or options for fading and all that. What you see as colour on the pony is essentially an outline of a 'pony-shaped object' with a colour fill
Illustrator, Flash and Inkscape (which is free) are examples of vector art programs. From the outset I've been going for show accurate, which is why I chose to train myself in vector art, because MLP is animated in Flash
Raster art programs however, are more like proper pen and paper. The moment you draw a line, it's set in stone already. There's no such thing as going back to select the line and adjusting it. If you drew it wrong the only thing you can do is either undo it or erase part of it and try to fix it. The upside of this however, is that you can do a lot of great things with airbrushes and pen tools and blur tools and all that good stuff, that's why raster artists tend to generate pieces that have great shading and shadows and all that. This is the reason why I have a great respect for artists who use raster programs but yet are able to make vector-quality artwork, because the sheer amount of precision required is just amazing to me.
The majority of the programs out there are raster, Paint Tool SAI, CorelDraw, Photoshop, GIMP and MSPaint are all raster.
I have Paint Tool SAI, but have not figured out how to use it yet