The APR and the APY are both used in order to describe the interest rate that is being charged on an investment or the loan. APR is going to focus on your yearly rate, and it will not be focused on your compound interest. APY will make use of your compound interest so that you will know how much you would need to pay or how much you can earn based on the details that you have placed.
Take note that these two things are very helpful, especially when you are trying to learn more details about student loans in general. The details can be very confusing in the beginning, but with the information that you have learned, it will be easier to make the best choice.