Add a thesis statement to the beginning of your outline. The thesis explains the main purpose of your essay and is included in the first paragraph, or introduction.
Include the main points that you will cover in your essay as points A, B and C. For example, in an essay about the necessity of war, you might include points about how war can be justified by the need to prevent attacks, respond to attacks, and govern and make decisions in the interest of a government's own people.
Gather evidence to support your main points. The evidence will be used in the outline and then in your essay to prove or explain your purpose. Use books and articles on the subject to gather your evidence.
Write in the evidence you find under the appropriate point in your outline. For example, when reading a book on World War II, you might find evidence that backs up your point about how needing to prevent future attacks and invasions can be a justification for war. This information would be added to your outline beneath your first point, or point A. Each sub-point can be labeled with numbers. This would be sub-point number 1 under point A.
Continue adding sub-points until you have at least three sub-points per main point that can be backed up by evidence. Remember to keep track of where the evidence came from to make it easier to site it in your essay.