But in more seriousness, it’s complicated. Jojo is divided into “Parts” that follow the Joestar family line. Each part typically follows the next generation having their own story.
Part 1 is about Jonathan Joestar, and in a nutshell is about the rivalry between him and his adoptive brother Dio. This rivalry will become a through-line throughout the series as Dio either becomes a recurring antagonist or his actions/followers set the plot.
Part 2 is about Jonathan’s grandson Joseph. His story in a nutshell is about stopping the ancient “Pillar Men” from enslaving humanity.
Part 3 is about Joseph’s grandson Jotaro. His story in a nutshell is about stopping a revived vampirized Dio from taking over the world. It’s also where the series’ iconic Stands are introduced, oddly enough.
Part 4 is about Joseph’s illegitimate son Josuke…so Jotaro’s uncle. That’s not the only this Part mixes up the formula as this one lowers the stakes immensely, in a nutshell being about Josuke stopping a serial killer accosting his home town.
Part 5 is about Dio’s son Giorno, surprisingly enough. His story in a nutshell is about him trying to become the head of his mafia organization.
“In a nutshell” is needed because the plot can get pretty crazy at points. There’s a surprising amount of story and plots that take place between the start and end of each Part.