Most students when they come to the USA struggle to purchase things like a cell phone on contract or obtain a credit card from an American bank – and the main reason is that everything in the USA is based around your credit score. Have no score or a bad score and you will struggle to get every day things like a cell phone or credit card! (I know, I have been there!)
To help you out, I have found an article which talks about credit, how it is judged and what you can do to build your score:
One tip that worked for me to build my credit in the USA was to obtain a small loan with someone who has a good credit score, a joint application. This meant the loan was approved as they looked at the main applicants good credit score but when repayments were made both reports were credited with good, on-time payments – this allowed me to build my credit very slowly until I was approved about a year later for my own credit card.