Gorgias tries to defend his ideas on what rhetoric stands for and tries to define the term to Socrates.  Socrates allows Gorgias to hang himself with his definition of the term and Socrates pokes holes into Gorgias ideas.   

SOCRATES: I am glad to hear it; answer me in like manner about rhetoric: with what is rhetoric concerned?

GORGIAS: With discourse.

SOCRATES: What sort of discourse, Gorgias?–such discourse as would teach the sick under what treatment they might get well?

Socrates questions how rhetoric is used in different types of fields like medicine or gymnastics and does a doctor know how to treat illness best or could a rhetorician improve a person but there language skills alone.  It seems that Socrates questions how powerful a person who knows rhetoric could be that by mere words a person could heal or convince a person to do bad things.

But there are other arts which work wholly through the medium of language, and require either no action or very little, as, for example, the arts of arithmetic, of calculation, of geometry, and of playing draughts; in some of these speech is pretty nearly co-extensive with action, but in most of them the verbal element is greater–they depend wholly on words for their efficacy and power: and I take your meaning to be that rhetoric is an art of this latter sort?

That rhetoric creates power with its spoken meaning that without rhetoric certain jobs could not be done proving that the spoken word has powerful uses in our society.  Socrates and Gorgias also argue about using rhetoric for means that are evil but convincing people to do things they might not want to but by using persuasive rhetoric techniques you force people into a decision they do not want to make.

SOCRATES: Now I think, Gorgias, that you have very accurately explained what you conceive to be the art of rhetoric; and you mean to say, if I am not mistaken, that rhetoric is the artificer of persuasion, having this and no other business, and that this is her crown and end. Do you know any other effect of rhetoric over and above that of producing persuasion?

GORGIAS: No: the definition seems to me very fair, Socrates; for persuasion is the chief end of rhetoric.

Socrates tries to argue that a philosophers job is more noble or better then a rhetorician since they use devices to persuade people and a philosopher is much more open to discussion.  At the end of the discussion Socrates admits that both sides are fair and noble in the pursuit and discussion of society and language.

Overall the broader picture is that rhetoric uses persuasion to get an idea across to who ever is in the audience.  How well that idea is processed by said audience depends on the art of the persuader.  Socrates concludes that rhetoric can be an art form because it uses words to convince or define situations or jobs.  How well language is constructed depends on how it is crafted, further proving rhetoric a s a type of art.  How artful it is used depends on the user.