What is tracker?!?!?

Okay, so i was checking my computer, and i found a tracker cookie? I did a little further research and found that you can only get one if you visit sites. I have no interests in , nor have I myself been on any site. At least not intentionally. This my own personal laptop, so not very many people get on it besides my friends and I, and although some of my friends do watch , i doubt they would on my laptop. anyways, I dont know if or how to get these cookie things off my computer, and i cant ask my parents for help because i dont know if theyll believe me when i say im not watching . Can i get these cookies off, and is there any way to prevent them? what do they do, anyways? could i have possibly have gotten this cookie from anywhere else?