Everything is made of plain filled paths, the character, the background, the graffiti, everything. I first drew a sketch on paper, then put the line-work on top and finally added color and simple flat shading. Does this answer your question?
Oh, I know that in the right hands Inkscape can do far more impressive things, graffiti and anything else. I'm everything but a graffiti artist, just scribbled a bit and tried to get something together that looked okay. When vectorizing the sketch I tried to keep things neat and clean. Nothing overly exciting but I kinda like the result.
Good luck with the program. You shouldn't have too much trouble getting used to how things work. But if you do, there are tons of tutorials online and at the official unofficial (hahaha) forum you should be able to find help, too. Btw. I'm self-taught, too.