Can someone tell me how to create icons?

As the title suggests, I would like some help with creating icons to democracy 4, since I am trying to mod that game. However, the problem is that I do not really know how to create icons. I am new to modding, so therefore I would like some help. Since I am new to modding, can someone tell me in a simple, but still in detail (if that makes sense), how to create icons?