This is your income. This is your other financial obligations. It's harder for those with no previous credit to borrow money than it is for those who have established good credit. The best way to establish credit is to pay your bills on time. Often it is easier to get a secured loan than an unsecured loan.
Auto loans are a good place to start.
Getting a parent to co-sign a loan can help you over the hurdle of getting your fist loan. Some companies offer what looks like a credit card but is actually secured by money you give them in advance. You are, in effect, borrowing against your own money-and paying interest to do it. Although this is not a good financial deal, it can help you establish credit. The key here is to make your payments on time.