Er, what the title says. 
I’m note quite sure what a US-ians means. US Asians?
Anyway One rejection from a credit card company probably won’t effect your credit rating. If you are rejected from several CC companies they (the credit bureaus) might mark this on your credit report.
Any time you apply for credit, the creditors look at your report, which does ding it for a time. So, apply sparingly. I don’t think rejections show up though (thank Og).
An inquiry from a potential creditor can affect your score. How much depends on the scoring model used by the particular credit bureau. AFAIK rejections are not reported directly to the reporting agencies but if there’s an inquiry from Credit Cardco and then no corresponding account for a Credit Cardco card, other potential creditors may draw the obvious conclusion.
Multiple credit inquiries will definitiely lower your overall score (an exception being multiple inquiries for things like mortgages, in which multiple inquiries in a short timeframe are treated as a single request).
The answer is “maybe”.
Sometimes your score goes down when you apply for something, but sometimes it doesn’t.
This is due to the whole system being fiendishly complex.
Inquiries hurt people with good credit more than people with bad credit.
Which is one way of saying that if your credit really stinks, nothing is going to make it any worse.
That’s part of what I’m saying. Another thing I’d like to say is… once your credit score gets stratospheric, you’ll see large point fluctuations for stuff that is incredibly trivial.
Credit scoring is weird, but when Fair Isaac decides if you’re an “800” or an “850”, they’re trying to handicap whether or not there’s a 1 in 1000 chance you’ll default on a given loan versus a 3 in 1000 chance.
There seems to be a world of difference inbetween 600 and 700. People right beneath 600 usually have enough crap on their reports that no sane non-predatory lender would touch them.
People on the high side of 660 or so generally have no substantial recent nasties on their reports, and a layman looking at their credit report would generally see them as persons you might reasonably expect to receive your money back from if you gave them a loan.