Yeah, and to learn how to 'make mods' you need to learn how to do whatever your thinking of.
Are you thinking of making 3d models of cars and importing them? Making tracks? It all requires basic 3d knowledge and how things are produced, rendered and implemented into games.
I suspect the reason you haven't found a simple tutorial on 'how to make mods for rFactor' is because its not a simple, straight forward thing to do - otherwise everyone would be doing it.