@katie364 First of all, it's free if you have a scholarship from the state which is given depending on your family's income, and even if you don't have it, it's pretty cheap (170 euros a year in my university) For the classes we have CM (cours magistraux) which are big classes in an amphitheater with a lot of people, and TD (Travaux Dirigés) which are classes in a smaller group (=20/30 people max, can be less). For your exams it depends on the kind of thing you're studying. You could have exams at the end of each semesters(there's two in France) or a mix of small exams during the semesters and big exams at the end. I don't really know what else you would like to know so if there is anything in particular feel free to ask!
@katie364 heyy sorry for answering this late I had deleted the app, I don't know if this can still help you but anyways here's the answer : semester 1 is from September to December and semester 2 from January to may/June. In my university, each CM (and TD) are 1h30, I guess it depends on where you are but it's around this length