Consider the dihydrogen molecule, #H-H#, this is composed of #2xxdotH# radicals... The electrons are shared between the two hydrogen nuclei to form a covalent bond......
Let's go to another example, the benzene molecule, #C_6H_6#; we gots #6xx4_"carbon electrons"+6xx1_"hydrogen electrons"# to share over 12 centres.......
The #C-H# electrons are localized between carbon and hydrogen, there are conceived to be #6xxC-C#, another 12 electrons; the remaining 6 electrons are conceived to be delocalized over the carbon ring, i.e. delocalized, and not associated with any particular carbon.....our representations of the benzene ring reflect this....
But these days this one is more common.....
Note that both pictures purport to represent the benzene molecule, but we understand that the #6pi# electrons are delocalized around the entire ring.
