Don't apologize for the questions. That's what this whole forum is all about... just make sure you stick around long enough to help everyone else that will go through the same problems as you.
Anyways, Tank pressure tells you how much pressure is in the tank. You don't really need to worry much about that one. Regulated pressure is what you're looking at to set your air pressure. Depending on that knob, it might just spin to adjust the pressure, or you might have to pull it up and spin it, or push it down and spin it. I have the same brand of compressor, and the one that came on mine (different model) you have to pull up and spin. When you're setting your air pressure, keep your airbrush handy, so you can release the air pressure from the regulator. Otherwise you'll walk away thinking its set at 15 psi, but that was really just what was left in the hose and after you start airbrushing, it will drop to zero. Hope that makes sense.
Your compressor will start and stop as you airbrush. When the pressure drops below the minimum pressure in the tank... probably somewhere around 85-90 psi, it will fill the tank again to 125 psi, then shut off and wiat till the pressure drops again.
when I'm done for the night, I just leave it on, but once a week I'll drain the tank. you don't want to let water water build up and sit in there. It causes rust and will eventually eat a hole in the tank. Some people drain it every day, but I'm happy if I remember to do it every week.