When he arrives for a year in america, a reserved french student must learn to adapt to make the most out of the experience.

That's the thing.? If you want to write a sort of memoir, or biography, that's fine, maybe you don't need a logline. If you want to write a marketeable fiction, you need conflict, clear goal, a sharp logline that states all very clearly. Have a look at the examples section. See how clear the conflict, the goal and everything are.

Thank you Moviefreak81. Would using "to open up" instead of "to adapt" be better?

I thought of it all about a novel telling the story of a french boy spending a year abroad in the U.S. in a host family and in an american high school, with all the ups and downs that come with such an experience. I don't really know what goal could come of it except experiencing it. I did an exchange like that for 4 months and I didn't really have a goal in mind except becoming bilingual and experiencing life in the U.S.

To add to Foxtrot25's comment, I can't see a hook there, and the stakes can be improved. For instance, "learn to adapt" could be made more specific (more specific is usually better in most cases) and "make most out of the experience" while relevant to the character, how can it be relevant to the audience as well? The most out of the experience could be in the end something that the audience could care about right a way? Like being opened to love, friendship... overcome some prejudice...?