Part 1, Phantom Blood, is set in the far past (I think like Victorian or whatever) and follows Jonathan Joestar, the first Jojo of the series (As you can see, all Jojos get their nickname because of their syllables). He is an English gentleman who's life is intruded by a bad kid named Dio. His dad adopts Dio as he slowly ruins Jonathan's life. Dio eventually uses a stone mask to turn himself into a vampire as he tries to conquer the world. Jonathan learns Hamon (Or Ripple, if you are a pleb) from this guy named Zeppeli as they try to stop him. Jonathan mainly uses pure strength to defeat his enemies.
Part 2, Battle Tendency, is set farther in the future and starts of in the States. It follows the grandson of Jonathan, Joseph Joestar (my personal favorite Jojo). He is funny and quirky and crafty as he outsmarts his enemies and predicts their lines (it's kind of a meme). He is tasked with stopping the Pillarmen, near immortal beings that (I think, I kind of forgot) want to rule the world as well and use humankind as a food source. The three (there are actually four, including Santana, but he is forgotten for the rest of the series) are Wamuu, Esidisi, and Kars. He is joined by a descendant of Zeppeli, Caesar Zeppeli.
Part 3, Stardust Crusaders, is one of the more popular ones and follows the grandson of Joseph, Jotaro Kujo (Or Kujo Jotaro, hence the Jojo). He is a badass big buff boi as he travels to Egypt to save his mother from her Stand, a being that comes from the mental energy of a person or animal (yes, animal. Also, they're basically Personas). He uses his own Stand, Star Platinum to fight DIO (with all caps) and his minions. Joseph also returns as an old man to assist him with this "crusade" against DIO. He is also joined by a few more Stand Users. Jotaro mainly uses impossible solutions and strength to beat the living shit out of his enemies.
Oki, let me continue in another box