otheractor is poiter to actor which have component you overlap with
othercomponent is pointer to component you overlap
Otherbodyindex not exacly sure but definitly is a body index of component you overlaping with
In UE terminology “other” means something that cause the event 
You can use those to code some kind of interaction between overlaping components.
hi , what are otheractor , othercomp , other body index parameters , where can we use them , are they output parameters or ?
ty , why do examples cast other actor to Cast to character , what is purpose here?
Most likely because those parameters are declered as parent class pointers like UPrimitveComponent or AActor so it can give you any actor and any primitve component pointer. If you want to use function of some child class you will need to cast. You can detect what actor or component you dealing with thanks by function IsA ()