A chronology is like a timeline: it tells what happened when. A chronology of your day would begin when you wake up and end when you go to sleep. Hopefully, something interesting happened in between.
Khronos is the Greek word for "time" and that's where chronology comes from. If a movie has a lot of flashbacks or doesn't tell a story straight through from beginning to end, you might have to give it some thought in order to put together a chronology of events. If you are a detective, a correct chronology could be important to solving your case.