Prometheus Label

Hi everybody,
i have question regarding to prometheus config.
i have in total 4 crodsec instances running. all those instances has metrics enabled and working.
so i setup the crawler in prometheus and i get the data not a problem until here.
so now my questions what are the labels used for and if i label machine with a string all instances get the same label. did i need it? who did i lable it dynamic to the hostname?
thanks in advanced