Tracking pixel?

Hello guys so I am very interested in how analytics for websites work i.e page views and what not. I understand its through the use of a pixel, however I am struggling to find any resources online on how to build such a thing or how it works in general. I am not trying to build something crazy, but just trying to learn. Any one got any resources I can look at?

I know node js and django if that helps in anyway.

Thanks