World ends because of humans were using braindead mothers and their fetuses which ccaused a soul fail to move on into the world of the dead creating the first BT
Beach is your own personal limbo, if you fail to move on you become a BT
People live underneath the earth because touching a BT causes a nucular reaction
Rain bad
And people that can access their beach and leave into the world of the living gain supah powers because supah powers are cool or something.
Troy is literally Kafka
BBs can sense BTs because they live between the world of the death and the living

Did i missed anything? seems pretty self explanatory to me