The headings in an APA paper are formatted as follows:
Heading Level 1 (Bold and Centred)
Heading Level 2 (Bold and Left-Justified)
Heading Level 3. (Bold, Indented and Followed by Period). Text starts here and continues on the next line ...
Heading Level 4. (Bold, Italicized, Indented and Followed by Period). Text starts here and continues on the next line ...
Heading Level 5. (Italicized, Indented and Followed by Period). Text starts here and continues on the next line ...
For more information about headings in APA style, see the APA Style Blog.