The final sentence of the introduction is one of the most important sentences of your essay. It is called the Thesis Statement and it tells the reader what you are going to talk about in your essay. For example, if your essay is: "Smoking should be banned. Discuss both sides of this argument." Your first two sentences may be: "There are many factors in the world that can affect our health. One of the most commonly-mentioned factors is smoking, which has been researched globally."

My Thesis Statement could be: "This essay will discuss the problems associated with smoking and consider the support for and against banning smoking."