Namely boobies

Can anyone explain bra sizes to me please?

How do they work, whats the smallest size, and if possible an example pic, and whats the medium and largest size, again with and example pic if possible.

Ive never really understood this concept between 34dd and all the other things other than reading that some models have '34dd' breasts.

Any help the female GWW Community members could offer me on this topic would be appreciated

Regards,

Lee