Because the application is free and non-commercial, the interface has been designed to be completely easy to use. In other words, you are fooling around with it and to start creating all kinds of abominations, so do not need a tutorial of any kind. After a while, it is usually sufficient to simply drag elements from one place to another, and not much else.
Now, for users who want to get more serious about Meshmixer, many tutorials on the official website that'll help you to create different models. You'll not only PDF Manuals, but how YouTube videos. That this was not enough, the official website also has some additional tricks and advice.
MeshMixer to create a 3D object tool potential, thanks to a matter of minutes you will be able to create complex models are fulfilled. All you need is a little imagination and a minimal amount of patience.