Bombs are destructive due to the fact that they release a large amount of energy through a chemical reaction into a very small volume of space. This manifests itself in hot, expanding gas that pushes outward, creating a shock wave and launching shrapnel.
To create an explosion a person needs the same ingredients necessary to create a fire (combustible material, oxygen and a source of ignition). In the case of a bomb, the oxygen and combustible material are bound together so that everything happens faster. A fuel and an oxidizer are combined chemically to create a new compound that when detonated will explode at anywhere from 9,000 to 27,500 feet per second.