Section 3.02, Organizing a Manuscript with Headings, and 3.03, Levels of Headings (p.62-63), cover how to use headings and what they should look like. Table 3.1 specifically shows the five levels of headings and how they should be formatted.
For examples of the headings, see Figure 2.1, Sample One-Experiment Paper. Page 44 shows examples of identifying subsections within the Method section.
All information and page number references are based on the 6th edition of the Publication Manual of the American Psychological Association (2009/10).
Need a copy of the Publication Manual? Click here for details. See Also: APA Style Guide to Electronic References, Sixth Edition