If you have the right to this monthly help, you can read what you need on this site. Do the paperwork as fast as possible, because you will not get the money for the months before you applied. It can be a very good idea for you to apply for this even though you only stay for a short time in France, since it can be from 0-400€ depending on your monthly income, the appartement etc.
But one thing that is very important to know is; the CAF is based on your income two years ago. For most of you, coming to France after your studies, you might didn't have a job, or only a part-time job which means that your monthly income was very low. This means that your CAF will be very high. But, if you start your studies after two years of a full-time work, your CAF will change and be very low!
An example; you come to France in January 2011 and you work full time for one or two years. In September 2013 you decide to study in France, which means that your income will decrease - you will earn less than before. This doesn't mean that the CAF will raise! Since the CAF is based on what you earned two years ago, and you had a full-time job, you might only get 20 or 40€ a month! It's very important to know this since it might not be logic for everyone and it can ruin the budget you made.
