By convention, there must be at least two entries at each level. If there is only one, it should be combined with the higher level that includes it. In this part of the outline, I'll ignore that rule, so that I can show you the numbering at each level. The third level is numbered with Arabic numerals. After the fifth level, you're on your own.
Classical outlines are of two forms.
This outline is a sentence outline. Topic outlines consist of words or phrases, not complete sentences. Outlining is a good way to study new material. When you outline something, you have to figure out the way the information is structured. Outlining focuses your attention on the main points, so that they aren't hidden by the details.