How do we describe delocalization is a difficult question to answer. Terms such as resonance, mesomerism, conjugation, and delocalization are only a few of the ones you will find in books that cover the subject.The term 'resonance' suggests that the structure vibrates rapidly between localized structures.
However I have found that using simple explanations is an effective way of describing them conjugation and delocalization: conjugation focuses on the sequence of alternating single and double bonds while delocalization focuses on the molecular orbitals covering the whole system. Electrons are delocalized over the whole of a conjugated system.
Kekule was the first scientist to suggest a sensible structure for benzene.Previous attempts had been quickly floored by others.The carbons are arranged in a hexagon, and he suggested alternating double and single bonds between them. Each carbon atom has a hydrogen attached to it. This diagram is often simplified by leaving out all the carbon and hydrogen atoms!
In diagrams of this sort, there is a carbon atom at each corner. You have to count the bonds leaving each carbon to work out how many hydrogens there are attached to it. In this case, each carbon has three bonds leaving it. Because carbon atoms form four bonds, that means you are a bond missing - and that must be attached to a hydrogen atom.
Although the Kekule structure was a good attempt in its time, there are serious problems with it Because of the three double bonds, you might expect benzene to have reactions like ethene - only more so! Ethene undergoes addition reactions in which one of the two bonds joining the carbon atoms breaks, and the electrons are used to bond with additional atoms. Benzene rarely does this. Instead, it usually undergoes substitution reactions in which one of the hydrogen atoms is replaced by something new.