An outline is a hierarchical list of words, phrases or sentences grouped according to their topics or positions in a piece of writing. Each point in an outline may or may not have sub-points that describe it at a finer level of detail. Sub-points are indented further than the points they describe and labeled differently. A standard outline format labels the top-level items with capital Roman numerals (I, II, III), the next with capital letters (A, B, C), the third with lowercase Roman numerals, and the fourth with lowercase letters.
The items at the same level of an outline should be parallel to one another in their level of detail. For example, if you have a high-level outline that divides an essay about chores into three main sections, they should be something like "Cooking," "Cleaning" and "Household Repairs," instead of "Cleaning," "Sweeping" and "Sweeping My Bedroom," which talk about the same topic in increasing detail. The more detailed topics should go under the broader topics as sub-points.
Creating an outline can help you plan the structure of an essay, story or paper to make sure it is organized in a logical fashion. Start by brainstorming all of the points you want to make, at any level of detail. When you're done, start grouping related points, then listing them under the category that describes all of them. You can group categories under even higher-level categories, then write out your groupings in outline form.
You can also use outlines to help you make sense of a piece of writing created by someone else. The "one sentence per paragraph" method is a good way to create an analytical outline. Summarize each paragraph in the work you are analyzing into one sentence. Group the sentences into unified categories, and label each category with a broader sentence that summarizes a whole section of the work. Creating an outline using this method will not only help you understand the content and structure of the work, but will also produce a detailed summary for future reference.