How do I properly use an airbrush?

That is supposed to be Corvus Black (Citadel). I have properly cleaned the airbrush. My problem is how do I get the right amount of paint in the airbrush for it to come out good. Do I dilute it in the airbrush with water or thinner? Does normal thinner work or should I invest in some airbrush thinner. Airbrush is brand new BTW.