Many thanks to your explanation! Now I get the idea of the rest frame thanks to you.... Actually it reminds me of an exercise I did in high school on this topic (just replace the car by a bike). I think I will try to dig in other questions to get a better understanding. Thanks a lot.

Thanks for your answer. According to your description I would ask again : then what's hapoening for light itself? Does time and duration decrease to 0?

Thanks for your references. Unfortunately, I don't think I have enough knowledge on the subject to understand how those questions are linked to mine. I'm sorry. I think I will need some more time to really get into relativity.