The function of an argumentative essay is to show that your assertion (opinion, theory, hypothesis) about some phenomenon or phenomena is correct or more truthful than others'. The art of argumentation is not an easy skill to acquire. Many people might think that if one simply has an opinion, one can argue it successfully, and these folks are always surprised when others don't agree with them because their logic seems so correct. Argumentative writing is the act of forming reasons, making inductions, drawing conclusions, and applying them to the case in discussion; the operation of inferring propositions, not known or admitted as true, from facts or principles known, admitted, or proved to be true. It clearly explains the process of your reasoning from the known or assumed to the unknown. Without doing this you do not have an argument, you have only an assertion, an essay that is just your unsubstantiated opinion.
One option is to organize your essay from general to particular . For example, if you were describing the new Big Tex at the State Fair of Texas, you might start out by describing the setting - the smell of the corn dogs frying, the crowds of people, the happy children dodging in and out of the midway games - then get into his grandiose size - after all, everything is bigger in Texas, right? After that, you describe the details: his new crisp, white, pearl snap shirt, his blue jeans tucked into cowboy boots, adorned up top with his signature belt buckle, and so on.