well first of all there are many different types of bombs, the simplest work by ignition of an explosive which can be controlled by timer devices or by remote control. Atom bombs work by triggering splitting of highly reactive atoms which releases an enormous amount of energy. A similar process happens in our sun and the stars.
You want to make one? :/ They have an explosive in and they are then delivered to the ‘enemy’ either via rocket or gravity or some other method! An explosive is a material that has the capability of releasing a large amount of energy in a short time.