Simple explanation about FORK

Loving the concept of blockchain and cryptocurrency, pushes me to learn and understand more about it.
I use to do it by watching videos and reading articles.
Since FORK is something that happens more often, I wanted to understand it better in plain words.
I have crossed this article and now I understand much better.
Maybe others will find it helpful too:
https://cointelegraph.com/news/dont-fear-forks-theres-only-one-bitcoin