All student loans have grace periods -- the time between when you take out a loan and when you must begin paying it back -- which vary based on the loan. For government loans, you generally have six to nine months after graduation before you must make a payment.
Meanwhile, suppose you have a job in college, get a job immediately after college or come into a wad of cash. It's OK to make payments before the grace period ends. Even if you can't make full payments or make a payment every month, you can pay on the interest, which, depending on your loan, may begin to accrue before you finish school.
Plus, getting in the habit of making payments as soon as you can means you'll be that much farther ahead once the actual loan repayment period begins. Whether you make early payments or not, know what the grace period is for each loan you have. You don't want to miss the first must-pay payment.