its a percentage, like 10-20 percent of the cells are abnormal in cin1, 30 to 40 in cin2, and so on (those are just random numbers, but something like that)
cin 1 is very low and can sometimes go away by itself. generally you dont treat that, just monitor it closely and sometimes cryo will remove the small amounts. but you need to get frequent paps to make sure it doesn't advance, and if it does, treat it earlier while its easier to clear.
No big deal, i had cin3 and just got my followup pap/biopsy clear after my treatment, even at advanced stages it can be totally taken care of. just monitor closely and dont skip appointments