The Roadrunner's Guide to English: Essay Structure
You can imagine the structure of an essay looking something like the diagram below.
At the top is your introductory paragraph, which starts broad and narrows down over the course of a few sentences to your very specific thesis statement, which is the last sentence in the paragraph.
Then, the middle or body paragraphs are "fat" with lots of specific details in each to illustrate your points.
Finally, the conclusion paragraph at the bottom starts narrowly, with a restatement of your thesis (be sure to word it differently than in the introduction - same idea, different words). Then the paragraph gets broader over the next few sentences, where you address the "so what" question. What is the broader significance of what you've been saying in the essay?