American Psychological Association (APA) format refers to a set of rules for writing social science papers. APA guidelines concern page formatting, headings, citations, statistics and other elements. Page margins in APA style should be 1 inch on all sides and body text should be left-justified, according to the seventh edition of the Publication Manual of the American Psychological Association.
Text Justification
Text justification, also called text alignment, refers to how text lines up between the vertical margins. If text is left-justified, as it should be in APA style, the text is aligned or even on the left margin and "ragged," or having uneven line lengths, on the right margin.
Left-justified text is the default in many word-processing programs. Right-justified text is even on the right margin and ragged on the left-margin. Centered text is ragged on both margins. Justified text is even on both margins and does not have a ragged edge, but justifying text sometimes creates awkward spaces between words.
Justifying Other Page Elements
While body text should be left-justified, other parts of your paper should be centered or right-justified. Your running header, for example, should be left-justified, while your page number should be right-justified.
The headings for your title page, author note, abstract, method, results, discussion, conclusion and references should be centered on the page. However, tables, figures, legends and captions should be left-justified.