During the age of All For One he released tons of telekinetic energy into the air and the people absorbed this power. Fast forward many years and the people who have descended from those who absorbed this power are known as Jedi, they work alongside the heroes. But of course where there is light there is dark. Some of those who do inherit this power known as the force have turned to the darkness and are known as the Sith. Quirks are also add-ons for the force but there is still a chance not to receive a quirk, those who do not receive quirks are outcasts even if they have the force. But those who do not inherit either are usually found dead.