This question is difficult to answer in one small space, but I will try. Paragraphs usually deal with one idea only with a topic sentence to inform the reader what the paragraph is about. The paragraph then explains, uses examples, and in general, uses the paragraph to prove the topic sentence. An essay is larger than a single paragraph, the most simple being a five paragraph essay with an introduction paragraph which contains a thesis statement, three body paragraphs, and a conclusion paragraph. The thesis statement controls the entire essay by stating what the essay will prove or demonstrate. The three body paragraphs will be the three main points used to prove the thesis, and then the conclusion paragraph is used to restate the thesis, reiterate the three main points and summarize the conclusion. No matter how long your essay is, whether five pages or five paragraphs, the idea is the same: to state what you are going to prove and then do so in your essay using good grammar, varied sentence complexity, good mechanics, and logical, coherent arguments.