Proof of parents' work when applying for a study visa and a letter of guarantee to bear the cost of studying in France.

There is no specific format, just write your parents' names, your name, and your parents are willing to pay all your study and living expenses in France. As for the work certificate, just ask your parents' company to open one and stamp the company's seal at the bottom. In fact, these two documents are not the most important materials for visas, as long as they are available. Good luck in your interview.