Remember Economics 101? Of course you don't! But in order to make smart decisions about how to handle those loan repayments, it's important to understand how your debt works (if you actually do remember Econ, skip to the next section).
Each month, your lender expects to you to cough up some money, called a monthly debt repayment. This repayment consists of two parts: principal (the original amount of the loan) and interest (the "extra" on top of the principal you have to pay each month). Interest is derived by applying the interest rate to your current outstanding principal. Like our favorite textbooks of yore, let's consider an example: Slim Charles took a loan of $10,000 from Proposition Joe to make a purchase in Bolivia. Being a savvy business man, Prop Joe said he could afford to lend the money at a 7% interest rate. Afterwards, he told Slim to pay him back $30 of the principle loan each month. So how much does he have to pay in the first month? Unfortunately, it's not $30—he must also pay the 7% interest on the principal, which in the first month is still $10,000. So he must pay $70 ($10,000 x 7%) in addition to the $30 principal payment. Thus, his total first month payments is $100, and his outstanding balance after this repayment is $9,970. See how much interest can hurt? (This clearly was a very simplified example--for starters, there will be a minimum principal repayment each month that you won't get to choose--but we do think this example gets the point across.) Well, it only gets worse if you miss a payment. Let's get back to Slim: Slim had a rough month on the corner and now he's broke. He still owes $10,000 and was supposed to repay $100 this month (principal plus interest), but he can't pay anything. Like most lenders, Prop Joe decides to capitalize the interest payment. This means that the interest Slim should have paid (e.g., $70) will now be added to his principal, thus making the new principal $10,070. And guess what? Next month, Prop Joe will use this new principal to calculate the interest payment (e.g., 7% of $10,070), so Slim will be even deeper in the pit. Among other reasons, capitalized interest is why you never want to skip a repayment installment. That's how debt balloons out of control (and, in Slim's case, how you might get rubbed out).
Links:
[1] http://www.gradspot.com/Money/Dealing with Debt/Student Debt Overview
[2] http://www.gradspot.com/Money/Dealing with Debt/Private Debt Consolidation and Debt Forgiveness