Generally, bumping a thread solely to draw attention to your ongoing problem is frowned upon, though I understand your frustration. And unfortunately, I'm no help because I'm not an airbrush guy (yet...

)
That being said, for anyone who's familiar with airbrushing, here's
accord99's original question/problem:
Ok, I tried out my Iwata HP-C airbrush today and apparently I don't know how to use it right.
I sprayed it at 13-15 PSI, I added my acrylic color into the paint cup then close the cap and pressed the trigger and pull back, but it kept squirting the paint out of the cap(little hole in the cap). It kept making a bubble sound, it's like mixing or something. My hairs and my head covers in white paint. I thought it was the needle but it's fine.
How do you use a normal Iwata HP-C
accord99: Have you tried simply Googling the problem?
I just did a search for "iwata hp-c problem" and it came back with over 1,500 results. Although it's nice when we can handle all our questions here within FFF, there may be some questions that folks here genuinely may not have an answer to. At that point, it might be in your best interest to see if there's any information out there--and then post the solution here for the next guy/gal who has a similar problem.
In short, I'm certainly not trying to encourage you to seek help elsewhere, but at the same time you shouldn't ignore readily available help that may already exist.