wouldn't know about tutorials, but the simplest way to start would be styrodur (styrofoam) and cardboard
it is easy to cut and to sand, inert for any paint (apart from dissolving enamel) and You can dump it and start anew if You are not content
just cut the main features with a sharp knife, sand it to shape and paint it
You can do flat portions by glueing any thickness of cardboard on
most important is not to spend too much doubts and just start
good luck