/sci/ - Science & Math

Hello /sci/, I'm having difficulty understanding infinity. I don't know if I'm going full retard or what.
If it is not growing but already is then why is it not measurable. Does it not exist? Although a circle has no end it is measurable. If it does exist why can't a value be assigned to it? I'm not trying to be a smartass, I'm genuinely confused.
tl;dr What do you guys use to understand infinity?