An emblazon is a pictorial image of a blazon, so an arms is emblazoned once it is drawn, coloured and guilded.
Emblazons are visual manifestations of heraldic insignia, typically displayed on shields or flags.
Because emblazons are awkward to work with, heraldry uses a specialized jargon called blazon to describe shields and flags. Persons skilled in heraldry can discuss shields entirely in blazon, without ever drawing the emblazons. As a noun, the word "blazon" is also used to refer to the heraldic description of a shield or flag.
The great advantage of blazon over plain English is that blazon terms are defined more precisely than English ones. As a result, one can describe a shield more accurately and in fewer words with blazon than one can in plain English.
The distinction between blazon and emblazon is an important one, since there is not a one-to-one correspondence between blazons and emblazons. In many cases, a particular emblazon can be blazoned (=described in heraldic language) in more than one way. And no two heraldic artists will emblazon (=draw) a given blazon in exactly the same way. But for well-designed heraldry, the blazon captures the important features of the emblazon, and, given a blazon, a trained heraldic artist should be able to produce a reasonable facsimile of the original emblazon.