I don't know what you mean by what did I use, but they are category icons. The icons are custom made by me using http://chrfb.deviantart.com/art/quot-ecqlipse-2-quot-PNG-59941546 icons. I can upload the 4 icons if you want it.
My question had like a double meaning. Firstly, how do you make those categories? I'm guessing they are like folders but you can use an icon instead of the default folder look. And secondly, where did you get those icons from, which you have already answered. And yes, I would be grateful if you could post those icons because they look simple but effective.