Hello I buy this line folower https://www.amazon.fr/Détection-Infrarouge-Suiveur-Dépistant-Panneau/dp/B07NY7MKJ8/ref=sr_1_2?__mk_fr_FR=ÅMÅŽÕÑ&crid=11RZCLNK0EEM5&keywords=suiveur+de+ligne+arduino&qid=1580755565&sprefix=suiveur+de+%2Caps%2C175&sr=8-2
but I dont know what library I can use can you help me please?
There is very little detail on the page linked to but it looks like there are simply 8 digital outputs from the sensor so you don't need a library to read them. You could, if you wished to save pins on the Arduino, use a shift register to read all 8 at once but even then you don't need a library to do it